delivered the opinion of the Court.

Title VII of the Civil Rights Act of 19641 makes unlawful, practices, procedures, or tests that “operate to 'freeze’ the status quo of prior discriminatory employment practices.” Griggs v. Duke Power Co., 401 U. S. 424, 430. To this rule, § 703 (h) of the Act, 42 U. S. C. § 2000e-2 (h), provides an exception:

“[I]t shall not be an unlawful employment practice for an employer to apply different standards of compensation, or different terms, conditions, or privileges of employment pursuant to a bona fide seniority . . . system, . . . provided that such differences are not the result of an intention to discriminate because of race....”

In Teamsters v. United States, 431 U. S. 324, 352, the Court held that “the unmistakable purpose of § 703 (h) was to make clear that the routine application of a bona fide seniority system would not be unlawful under Title VII . . . even where the employer’s pre-Act discrimination resulted in whites having greater existing seniority rights than Negroes.” 2

The present case concerns the application of § 703 (h) to a particular clause in a California brewery industry collective-bargaining agreement. That agreement accords greater benefits to “permanent” than to “temporary” employees, and the *601clause in question provides that a temporary employee must work at least 45 weeks in a single calendar year before he can become a permanent employee. The Court of Appeals for the Ninth Circuit held that the 45-week requirement was not a “seniority system” or part of a “seniority system” within the meaning of § 703 (h). 585 F. 2d 421. We granted cer-tiorari to consider the important question presented under Title YII of the Civil Rights Act of 1964. 442 U. S. 916.

I

In 1973, respondent Bryant (hereafter respondent), a Negro, filed a complaint in the United States District Court for the Northern District of California, on behalf of himself and other similarly situated Negroes, against the California Brewers Association and seven brewing companies (petitioners here), as well as against several unions. The complaint alleged that the defendants had discriminated against the respondent and other Negroes in violation of Title VII of the Civil Rights Act of 1964, 42 U. S. C. § 2000e et seq., and in violation of 42 U. S. C. § 1981.3

The complaint, as amended, alleged that the respondent had been intermittently employed since May 1968 as a temporary employee of one of the defendants, the Falstaff Brewing Corp. It charged that all the defendant employers had discriminated in the past against Negroes, that the unions had acted in concert with the employers in such discrimination, and that the unions had discriminated in referring applicants from hiring halls to the employers. The complaint further asserted that this historical discrimination was being perpetuated by the seniority and referral provisions of the collective-bargaining agreement (Agreement) that governed *602industrial relations at the plants of the seven defendant employers. In particular, the complaint alleged, the Agreement’s requirement that a temporary employee work 45 weeks in the industry in a single calendar year to reach permanent status had, as a practical matter, operated to preclude the respondent and the members of his putative class from achieving, or from a reasonable opportunity of achieving, permanent employee status.4 Finally, the complaint alleged that on at least one occasion one of the defendant unions had passed over the respondent in favor of more junior white workers in making referrals to job vacancies at a plant of one of the defendant employers.

The Agreement is a multiemployer collective-bargaining agreement negotiated more than 20 years ago, and thereafter updated, by the California Brewers Association (on behalf of the petitioner brewing companies) and the Teamsters Brewery and Soft Drink Workers Joint Board of California (on behalf of the defendant unions). The Agreement establishes several classes of employees and the respective rights of each with respect to hiring and layoffs. Three of these classes are pertinent here: “permanent,” “temporary,” and “new” employees.

A permanent employee is “any employee . . . who . . . has completed forty-five weeks of employment under this Agreement in one classification [5] in one calendar year as an employee of the brewing industry in [the State of California].” An employee who acquires permanent status re*603tains that status unless he “is not employed under this Agreement for any consecutive period of two (2) years. ...” 6 A temporary employee under the Agreement is “any person other than a permanent employee . . . who worked under this agreement ... in the preceding calendar year for at least sixty (60) working days. ...” A new employee is any employee who is not a permanent or temporary employee.

The rights of employees with respect to hiring and layoffs depend in substantial part on their status as permanent, temporary, or new employees.7 The Agreement requires that employees at a particular plant be laid off in the following order: new employees in reverse order of their seniority at the plant, temporary employees in reverse order of their plant seniority, and then permanent employees in reverse order of their plant seniority. Once laid off, employees are to be rehired in the reverse order from which they were laid off.

The Agreement also gives permanent employees special “bumping” rights. If a permanent employee is laid off at any plant subject to the Agreement, he may be dispatched by the union hiring hall to any other plant in the same local area with the right to replace the temporary or new employee with the lowest plant seniority at that plant.

Finally, the Agreement provides that each employer shall obtain employees through the local union hiring hall to fill needed vacancies. The hiring hall must dispatch laid-off workers to such an employer in the following order: first, employees of that employer in the order of their seniority with that employer; second, permanent employees registered in the area in order of their industry seniority; third, temporary employees in the order of their seniority in the industry; and *604fourth, new employees in the order of their industry seniority. The employer then “shall have full right of selection among” such employees.

The District Court granted the defendants’ motions to dismiss the complaint for failure to state a claim on which relief could be granted. No opinion accompanied this order. A divided panel of the Court of Appeals reversed, 585 F. 2d 421, concluding that the 45-week rule is not a “seniority system” or part of a “seniority system” within the meaning of § 703 (h) of Title VII. In the appellate court’s view the provision “lacks the fundamental component of such a system” which is “the concept that employment rights should increase as the length of an employee’s service increases.” 585 F. 2d, at 426. The court pointed out that under the Agreement some employees in the industry could acquire permanent status after a total of only 45 weeks of work if those weeks were served in one calendar year, while others “could work for many years and never attain permanent status because they were always terminated a few days before completing 45 weeks of work in any one year.” Id., at 426-427.

The Court of Appeals concluded that “while the collective bargaining agreement does contain a seniority system, the 45-week provision is not a part of it.” Id., at 427: *605Accordingly, the Court of Appeals remanded the case to the District Court to enable the respondent to prove that the 45-week provision has had a discriminatory impact on Negroes under the standards enunciated in Griggs v. Duke Power Co., 401 U. S. 424. 585 F. 2d, at 427-428.9

*604“The 45-week rule is simply a classification device to determine who enters the permanent employee seniority line and this function does not make the rule part of a seniority system. Otherwise any hiring policy (e. g., an academic degree requirement) or classification device (e. g., merit promotion) would become part of a seniority system merely because it affects who enters the seniority line.” Id., at 427, n. 11.8

*605II

Title VII does not define the term “seniority system,” and no comprehensive definition of the phrase emerges from the legislative history of § 703 (h) .10 Moreover, our cases have not purported to delineate the contours of its meaning.11 It is appropriate, therefore, to begin with commonly accepted notions about “seniority” in industrial relations, and to consider those concepts in the context of Title YII and this country’s labor policy.

In the area of labor relations, “seniority” is a term that connotes length of employment.12 A “seniority system” is a *606scheme that, alone or in tandem with non-“seniority” criteria,13 allots to employees ever improving employment rights and benefits as their relative lengths of pertinent employment increase.14 Unlike other methods of allocating employment benefits and opportunities, such as subjective evaluations or educational requirements, the principal feature of any and every “seniority system” is that preferential treatment is dispensed on the basis of some measure of time served in employment.

Viewed as a whole, most of the relevant provisions of the Agreement before us in this case conform to these core concepts of “seniority.” Rights of temporary employees and rights of permanent employees are determined according to length of plant employment in some respects, and according to length of industry employment in other respects. Notwithstanding this fact, the Court of Appeals concluded that the 45-week rule should not be viewed, for purposes of § 703 (h), as part of what might otherwise be considered a “seniority system.” For the reasons that follow, we hold that this conclusion was incorrect.

First, by legislating with respect to “systems” 15 of seniority *607in § 703 (h), Congress in 1964 quite evidently intended to exempt from the normal operation of Title VII more than simply those components of any particular seniority scheme that, viewed in isolation, embody or effectuate the principle that length of employment will be rewarded. In order for any seniority system to operate at all, it has to contain ancillary rules that accomplish certain necessary functions, but which may not themselves be directly related to length of employment.16 For instance, every seniority system must include rules that delineate how and when the seniority time-clock begins ticking,17 as well as rules that specify how and when a particular person’s seniority may be forfeited.18 Every seniority system must also have rules that define which passages of time will “count” towards the accrual of seniority and which will not.19 Every seniority system must, moreover, contain rules that particularize the types of employment conditions that will be governed or influenced by seniority, and those that will not.20 Rules that serve these necessary pur*608poses do not fall outside § 703 (h) simply because they do not, in and of themselves, operate on the basis of some factor involving the passage of time.21

Second, Congress passed the Civil Rights Act of 1964 against the backdrop of this Nation’s longstanding labor policy of leaving to the chosen representatives of employers and employees the freedom through collective bargaining to establish conditions of employment applicable to a particular business or industrial environment. See generally Steelworkers v. Weber, 443 U. S. 193. It does not behoove a court to second-guess either that process or its products. Porter Co. v. NLRB, 397 U. S. 99. Seniority systems, reflecting as they do, not only the give and take of free collective bargaining, but also the specific characteristics of a particular business or industry, inevitably come in all sizes and shapes. See Ford Motor Co. v. Huffman, 345 U. S. 330; Aeronautical Lodge v. Campbell, 337 U. S. 521. As we made clear in the Teamsters case, seniority may be “measured in a number of ways” and the legislative history of § 703 (h) does not suggest that it was enacted to prefer any particular variety of seniority system over any other. 431 U. S., at 355, n. 41.

What has been said does not mean that § 703 (h) is to be given a scope that risks swallowing up Title YII’s otherwise broad prohibition of “practices, procedures, or tests” that disproportionately affect members of those groups that the Act protects. Significant freedom must be afforded employers and unions to create differing seniority systems. But that freedom must not be allowed to sweep within the ambit of § 703 (h) employment rules that depart fundamentally from commonly accepted notions concerning the acceptable contours of a seniority system, simply because those rules are dubbed “seniority” provisions or have some nexus to an arrangement that concededly operates on the basis of seniority. *609There can be no doubt, for instance, that a threshold requirement for entering a seniority track that took the form of an educational prerequisite would not be part of a “seniority system” within the intendment of § 703 (h).

The application of these principles to the case at hand is straightforward. The Agreement sets out, in relevant part, two parallel seniority ladders. One allocates the benefits due temporary employees; the other identifies the benefits owed permanent employees. The propriety under § 703 (h) of such parallel seniority tracks cannot be doubted after the Court’s decision in the Teamsters case. The collective-bargaining agreement at issue there allotted one set of benefits according to each employee’s total service with the company, and another set according to each employee’s service in a particular job category. Just as in that case the separation of seniority tracks did not derogate from the identification of the provisions as a “seniority system” under § 703 (h), so in the present case the fact that the system created by the Agreement establishes two or more seniority ladders does not prevent it from being a “seniority system” within the meaning of that section.

The 45-week rule, correspondingly, serves the needed function of establishing the threshold requirement for entry into the permanent-employee seniority track. As such, it performs the same function as did the employment rule in Teamsters that provided that a line driver began to accrue seniority for certain purposes only when he started to work as a line driver, even though he had previously spent years as a city driver for the same employer. In Teamsters, the Court expressed no reservation about the propriety of such a threshold rule for § 703 (h) purposes. There is no reason why the 45-week threshold requirement at issue here should be considered any differently.

The 45-week rule does not depart significantly from commonly accepted concepts of “seniority.” The rule is not an educational standard, an aptitude or physical test, or a stand*610ard that gives effect to subjectivity. Unlike such criteria, but like any “seniority” rule, the 45-week requirement focuses on length of employment.

Moreover, the rule does not distort the operation of the basic system established by the Agreement, which rewards employment longevity with heightened benefits. A temporary employee’s chances of achieving permanent status increase inevitably as his industry employment and seniority accumulate. The temporary employees with the most industry seniority have the first choice of new jobs within the industry available for temporary employees. Similarly, the temporary employees with the most plant seniority have the first choice of temporary employee jobs within their plant and enjoy the greatest security against “bumping” by permanent employees from nearby plants. As a general rule, therefore, the more seniority a temporary employee accumulates, the more likely it is that he will be able to satisfy the 45-week requirement. That the correlation between accumulated industry employment and acquisition of permanent employee status is imperfect does not mean that the 45-week requirement is not a component of the Agreement’s seniority system. Under any seniority system, contingencies such as illnesses and layoffs may interrupt the accrual of seniority and delay realization of the advantages dependent upon it.22

For these reasons, we conclude that the Court of Appeals was in error in holding that the 45-week rule is not a component of a “seniority system” within the meaning of § 703 (h) of Title VII of the Civil Rights Act of 1964. In the District Court the respondent will remain free to show that, in respect to the 45-week rule or in other respects, the se*611niority system established by the Agreement is not “bona fide,” or that the differences in employment conditions that it has produced are “the result of an intention to discriminate because of race.”

For the reasons stated, the judgment before us is vacated, and the case is remanded to the Court of Appeals for the Ninth Circuit for further proceedings consistent with this opinion.

It is so ordered.

with whom Mr. Justice Brennan and Mr. Justice Blackmun join, dissenting.

In the California brewing industry, an employee’s rights and benefits are largely dependent on whether he is a “permanent” employee within the meaning of the collective-bargaining agreement. Permanent employees are laid off after all other employees. If laid off at one facility, a permanent employee is permitted to replace the least senior nonperma-nent employee at any other covered facility within the local area. Permanent employees are selected before temporary employees to fill vacancies. They have exclusive rights to supplemental unemployment benefits upon layoff and receive higher wages and vacation pay for the same work performed by other employees. Permanent employees have first choice of vacation times, less rigorous requirements for qualifying for holiday pay, exclusive access to veterans’ reinstatement and seniority rights, and priority in assignment of overtime work among bottlers.

According to respondent Bryant’s complaint, no Negro has ever attained permanent employee status in the California brewing industry.1

*612The provision of the collective-bargaining agreement at issue here defines a permanent employee as one “who . . . has completed forty-five weeks of employment ... in one classification in one calendar year as an employee of the brewing industry in this State.” An employee who works 44 weeks per year for his entire working life remains a temporary employee. By contrast, an employee who works 45 weeks in his first year in the industry attains permanent employee status. This simple fact belies the Court’s conclusion that the 45-week requirement “does not depart significantly from commonly accepted concepts of ‘seniority.’ ” Ante, at 609. Since I am unable to agree that the provision at issue is part of a “seniority system” under § 703 (h) of Title VII, I dissent.

I

Neither Title VII nor its legislative history provides a comprehensive definition of the term “seniority system.”2 The Court is therefore correct in concluding that the term must be defined by reference to “commonly accepted notions about ‘seniority’ in industrial relations” and “in the context of Title VII and this country’s labor policy.” Ante, at 605. Those “commonly accepted notions,” however, do not lead to the Court’s holding today. And I believe that the relevant policies do not support that holding, but instead require that it be rejected.

The concept of “seniority” is not a complicated one. The fundamental principle, as the Court recognizes, ante, at 606, is that employee rights and benefits increase with length of service. This principle is reflected in the very definition of the term, as found in dictionaries'3 and treatises and articles in *613the field of industrial relations.4 To quote from a few of the sources on which the Court purports to rely today: “Seniority is a system of employment preference based on length of serv*614ice; employees with the longest service are given the greatest job security and the best opportunities for advancement.” Aaron, Reflections on the Legal Nature and Enforceability of Seniority Rights, 75 Harv. L. Rev. 1532, 1534 (1962). "The variations and combinations of seniority principles are very great, but in all cases the basic measure is length of service, with preference accorded to the senior worker.” Cooper & Sobol, Seniority and Testing under Fair Employment Laws: A General Approach to Objective Criteria of Hiring and Promotion, 82 Harv. L. Rev. 1598, 1602 (1969). “Seniority grants certain preferential treatment to long-service employees almost at the expense of short-service employees. . . . [Sjeniority is defined as length of service.” E. Beal, E. Wickersham, & P. Kienast, The Practice of Collective Bargaining 430 (1972).

It is hardly surprising that seniority has uniformly been defined in terms of cumulative length of service. No other definition could accord with the policies underlying the recognition of seniority rights. A seniority system provides an objective standard by which to ascertain employee rights and protections, thus reducing the likelihood of arbitrariness or caprice in employer decisions. At the same time, it promotes stability and certainty among employees, furnishing a predictable method' by which to measure future employment position. See, e. g., Sayles, Seniority: An Internal Union Problem, 30 Harv. Bus. Rev. 55 (1952); C. Golden & H. Ruttenberg, The Dynamics of Industrial Democracy 128-131 (1973); Cooper & Sobol, supra, at 1604^1605.

The Court concedes this general point, recognizing that a “ 'seniority system’ is a scheme that, alone or in tandem with non-'seniority’ criteria, allots to employees ever improving employment rights and benefits as their relative lengths of pertinent employment increase.” Ante, at 605-606 (footnote omitted). In my view, that concession is dispositive of this case. The principal effect of the 45-week requirement is to ensure that employee rights and benefits in the California *615brewing industry are not “ever improving” as length of service increases. Indeed, cumulative length of service is only incidentally relevant to the 45-week rule. The likelihood that a temporary employee will attain permanent employee status is largely unpredictable. The 45-week period, which is exclusive of vacation, leaves of absence, and time lost because of injury or sickness, represents almost 90% of the calendar year. Even if an employee is relatively senior among temporaries, his ability to work 45 weeks in a year will rest in large part on fortuities over which he has no control. The most obvious reason that employees have been prevented from attaining permanent employee status — a reason barely referred to by the Court — is that the brewing industry is a seasonal one. An employee may also be prevented from becoming permanent because of replacement by permanent employees or an employer’s unexpected decision to lay off a particular number of employees during the course of a year.5 It is no wonder that the accrual of seniority by temporary employees has not led with any regularity to the acquisition of permanent employee status.6 In sum, the 45-week rule does not have *616the feature of providing employees with a reasonably certain route by which to measure future employment position. So understood, the 45-week rule has very little to do with seniority, for it makes permanent status turn on fortuities over which the employee has no control, not on length of service with the employer or in the relevant unit.

The Court avoids this conclusion by little more than assertion. It observes that the 45-week rule acts as a threshold requirement for entry onto the seniority track composed of permanent employees, but eliminates the force of that observation with the inevitable concession that such threshold requirements are not necessarily entitled to § 703 (h) exemption.7 It notes that the 45-week requirement “focuses on length of employment,” and proceeds to the unexplained conclusion that it therefore “does not depart significantly from commonly accepted concepts of 'seniority.’ ” And it adds that more senior temporary employees tend to have a greater opportunity to obtain work and thus to attain permanent status through 45 weeks of employment in a calendar year.

The Court’s analysis, of course, is largely dependent on its conclusion that since the 45-week requirement is one measured by time of service, it does not depart from common concepts of seniority. That conclusion, however, is foreclosed by the Court’s own definition of a seniority system as one in which employee rights increase with cumulative length of *617service — not length of service within a calendar year. The mere fact that the 45-week rule is in some sense a measure of “time” does not demonstrate a valid relation to concepts of seniority. Such a conclusion would make the § 703 (h) exemption applicable to a rule under which permanent employee status is dependent on number of days served within a week, or hours served within a day.8

Nor is there much force to the suggestion that the 45-week requirement somehow becomes part of a seniority system because permanent employee status is more easily achieved by the more senior temporary employees. I could agree with the Court's decision if petitioners demonstrated that the collective-bargaining agreement actually operates to reward employees in order of cumulative length of service. But at this stage of the litigation there is no evidence that temporary employees attain permanent status in a way correlating even roughly with total length of employment. The mere possibility that senior temporary employees are more likely to work for 45 weeks is, in my view, insufficient.9 It might as well be said that a law conditioning permanent employee status on the attainment of a certain level of skill is a “seniority” provision since skills tend to increase with length of service. A temporary employee is always subject to a risk that for some reason *618beyond his control, he will be unable to work the full 45 weeks and be forced to start over again.

II

Since the 45-week rule operates as a threshold requirement with no relation to principles of seniority, I believe that the rule is for analytical purposes no different from an educational standard or physical test which, as the Court indicates, is plainly not entitled to § 703 (h) exemption. Accordingly, I think it clear that the 45-week requirement is not part of a “seniority system” within the meaning of § 703 (h). But if the question were perceived to be close, I would be guided by the familiar principle that exemptions to remedial statutes should be construed narrowly. “To extend an exemption to other than those plainly and unmistakably within its terms and spirit is to abuse the interpretative process and to frustrate the announced will of the people.” Phillips Co. v. Walling, 324 U. S. 490, 493 (1945). See, e. g., Group Life & Health Ins. Co. v. Royal Drug Co., 440 U. S. 205, 231 (1979); Abbott Laboratories v. Portland Retail Druggists Assn., 425 U. S. 1, 12 (1976); Peyton v. Rowe, 391 U. S. 54, 65 (1968). The effect of § 703 (h) is to exempt seniority systems from the general prohibition on practices which perpetuate the effects of racial discrimination. This exception is a limited one in derogation of the overarching purpose of Title VII, “the integration of blacks into the mainstream of American society,” Steelworkers v. Weber, 443 U. S. 193, 202 (1979). A statute designed to remedy the national disgrace of discrimination in employment should be interpreted generously to comport with its primary purpose; exemptions should be construed narrowly so as not to undermine the effect of the general prohibition. Today the Court not only refuses to apply this familiar principle of statutory construction, it does not even acknowledge it.

*619In my view, the Court’s holding is fundamentally at odds with the purposes of Title VII and the basic function of the § 703 (h) exemption. I dissent.10