concurring.

The decisions of this Court leave no doubt that a man’s time may, as a matter of law, be in the service of another *371though he be inactive. E. g., Armour & Co. v. Wantock, 323 U. S. 126. This is, practically speaking, the ordinary situation of employment in a “stand-by” capacity. United States v. Local 807, 315 U. S. 521, 535. The basis of a back-pay order under the National Labor Relations Act, 49 Stat. 449, 29 U. S. C. § 151, is precisely that. When the employer is liable for back pay, he is so liable because under the circumstances, though he has illegally discharged the employee, he still absorbs his time. Phelps Dodge Corp. v. Labor Board, 313 U. S. 177. In short, an employer must pay wages although, in violation of law, he has subjected his employee to enforced idleness. Since such compensation is in fact paid as wages, it is a plain disregard of the law for the.Social Security Board not to include such payments among the employees’ wages. Neither the terms of the Social Security Act, 49 Stat. 620, 53 Stat. 1360, 42 U. S. C. § 301, nor the implications of policy, comparable to some aspects of the Railway Labor Act, 44 Stat. 577, 48 Stat. 926, 48 Stat. 1185, 49 Stat. 1921, 54 Stat. 785, 45 U. S. C. § 151, give the Board judicially unreviewable authority to exclude from wages what as a matter of law are wages. And so I concur in the decision of the Court.

delivered the opinion of the Court.

A problem as to whether “back pay,” which is granted to an employee under the National Labor Relations Act, shall be treated as “wages” under the Social Security Act comes before us on this record. If such “back pay” is a wage payment, there is also at issue the proper allocation of such sums to the quarters of coverage for which the “back pay” was allowed.

The respondent, Joseph Nierotko, was found by the National Labor Relations Board to have been wrongfully, discharged for union activity by his employer, the Ford Motor Company, and was reinstated by that Board in his employment with directions for “back pay” for the period February 2, 1937, to September 25, 1939.1 The “back *360pay” was paid by the employer on July 18,1941. Thereafter Nierotko requested the Social Security Board to credit him in the sum of the “back pay” on his Old Age and Survivor’s Insurance account with the Board.2 In conformity with its minute of formal general action of March 27, 1942, the Board refused to credit Nierotko’s “back pay” as wages. On review of the Board’s decision,3 the district court upheld the Board. The circuit court of appeals reversed. 149 F. 2d 273. On account of the importance of the issues in the administration of the Social Security Act, we ¿ranted certiorari.4 326 U. S. 700; Judicial Code § 240.

During the period for which “back pay” was awarded respondent the federal old age .benefits were governed by Title II of the Social Security Act of 1935. 49 Stat. 622. As Title II of the Social Security Act Amendments of. 1939 became effective January 1, 1940 (53 Stat. 1362), the. actual payment of the “back wages” occurred thereafter. In our view the governing provisions which determine whether this “back pay” is wages are those of the earlier enactment.5

*361Wages are the basis for the administration of federal old age benefits. 49 Stat. 622. Only those who earn wages are eligible for benefits.6 The periods of time during which wages were earned are important and may be crucial on eligibility under either the original act or the Amendments of 1939. See. § 210 (c) and compare § 209 *362(g), 53 Stat. 1376.7 The benefits are financed by payments from employees and employers which are calculated on wages.* 12*****8 The Act defines “wages” for old age, benefits as follows:

“Sec. 210. When used in this title—

(a) The term ‘wages’ means all remuneration for employment, including the cash value of all remuneration paid in any medium other than cash; . . .”

*363Employment is defined thus:"

“(b) The term ‘employment’ means any service, of whatever nature, performed within the United States by an employee for his employer, except: — ”

The tax titles of the Social Security Act have identical definitions of wages and employment.9'. An employee under the Social Security Act is not specifically defined but the individual to whom the Act’s benefits are to be paid is one receiving “wages” for “employment” in accordance with § 210 (c) and employment is service by an “employee” to an “employer.” Obviously a sharply defined line between payments to employees which are wages and which are not is essential to proper administration.10

Under the National Labor Relations Act an employee is described as “any individual whose work has ceased . . . because of any unfair labor practice.” § 2 (3), 49 Stat. 450. The enforcement provisions of this Act under which Nierotko received his “back pay” allow the Labor Board to reinstate “employees with or without back pay.” § 10 (c). The purpose of the “back pay” allowance is to effectuate the policies of the Labor Act for the preservation of industrial peace.* 11

*364The purpose of the federal old age benefits of the Social Security Act is to provide funds through contributions by employer and employee for the decent support of elderly workmen who have ceased to labor.12 Eligibility for these benefits and their amount depends upon the total wages which the employee has received and the periods in which wages were paid.13 While the legislative history of the Social Security Act and its amendments or the language of the enactments themselves does not specifically deal with whether or not “back pay” under the Labor Act is to be treated as wages under the Social Security Act, we think it plain that an individual, who is an empk>3ree under the Labor Act and who receives “back pay” for a period of time during which he was wrongfully separated from his job, is entitled to have that award of back pay treated as wages under the Social Security Act definitions which define wages as “remuneration for employment” and employment as “any service . . . performed ... by an employee for his employer . . .”

Surely the “back pay” is “remuneration.” Under § 10 (c) of the Labor Act, the Labor Board acts for the public to vindicate the prohibitions of the Labor Act against unfair labor, practices (§ 8) and to protect the right of employees to self-organization which is declared by § 7.14 It i also true that, in requiring reparation to the employee through “back pay,” reparation is based upon the loss of wages which the employee has suffered from the •employer’s wrong. “Back pay” is not a fine or penalty imposed upon the employer by the Board. Reinstate*365ment and “back pay” are for the “protection of the employees and the redress of their grievances” to make them “whole.” Republic Steel Corp. v. Labor Board, 311 U. S. 7, 11, 12. “. . . a worker’s loss in wages and in general working conditions must be made whole.” Phelps Dodge Corp. v. Labor Board, 313 U. S. 177, 196. A worker is not given “back pay” by the Board equal to what he would have earned with the employer but for the unlawful discharge, but is given that sum less any net earnings during the time between discharge and reinstatement.15

Since Nierotko remained an employee under the definition of the Labor Act, although his employer had attempted to terminate the relationship, he had “employment” under that Act and we need consider further only whether under the Social Security Act its definition of employment, as “any service . . . performed ... by an employee for his employer,” covers what Nierotko did for the Ford Motor Company. The petitioner urges that Nierotko did not perform any service. It points out that Congress in considering the Social Security Act thought of benefits as related to “wages earned” for “work done.” 16 We are unable, however, to follow the Social Security Board in such a limited circumscription of the word “service.” The very words “any service . . . performed ... for his employer,” with the purpose of the Social Security Act in mind, import breadth of coverage. They admonish us against holding that “service” can be only productive activity. We think that “service” as used by Congress in this definitive phrase means not only work *366actually done but the entire employer-employee relationship for which compensation is paid to the employee by the employer.17

An argument against the interpretation which we give to “service performed” is the contrary ruling of the governmental agencies which are charged with the administration of the Social Security Act. Their competence *367and experience in this field command us to reflect before we decide contrary to their conclusion. The first administrative determination was apparently made in 1939 by an Office Decision of the Bureau of Internal Revenue on the problem of whether “back pay” under a Labor Board order was wages subject to tax under Titles VIII and IX of the Social Security Act which the Bureau collects.18 The back pay was held not to be subject as wages to the tax because no service was performed, the employer had tried to terminate the employment relationship and the allowance of back pay was discretionary with the Labor Board. Reliance for the conclusions was placed upon Agwilines, Inc. v. Labor Board, 87 F. 2d 146, which had held “back pay” a public reparation order and therefore not triable by jury as a private right for wages would have been. This position is maintained by the Social Security Board by minute of March 27,1942. It is followed by the National Labor Relations Board which at one time approved the retention by the employer of the tax on the employees’ back pay for transmission to the Treasury Department as a tax on wages but later reversed its position on the authority of the Office Decision to which reference has just been made. Re Pennsylvania Furnace & Iron Co., 13 N. L. R. B. 49, 53 (5), 54, 58.19

The Office Decision seems to us unsound. The portion of the Agwilines decision, which the Office Decision relied upon, was directed at the constitutional claim to a right of trial by jury. It stated that “back pay” was not a penalty or damages which a private individual might *368claim. But there is nothing in the opinion which supports the idea that the "back pay” award differs from other pay. Indeed the opinion said that “Congress has the right to eradicate them [unfair practices] as from the beginning.” 87 F. 2d at 151,1. c. We think the true relation of awards of “back pay” to compensation appears in the Republic Steel and Phelps-Dodge cases, hereinbefore discussed.20

But it is urged by petitioner that the administrative construction on the question of whether “back pay” is to be treated as wages should lead us to follow the agencies’ determination. There is a suggestion that the administrative decision should be treated as conclusive, and reliance for that argument is placed upon Labor Board v. Hearst Publications, 322 U. S. 111, 130, and Gray v. Powell, 314 U. S. 402, 411. In the acts which were construed in the cases just cited, as in the Social Security Act, the administrators of those acts were given power to reach preliminary conclusions as to coverage in the application of the respective acts. Each act contains a standardized phrase that Board findings supported by substantial evidence shall be conclusive.21 The validity of regulations is specifically reserved for judicial determination by the Social Security Act Amendments of 1939, § 205 (g).

The Social Security Board and the Treasury were compelled to decide, administratively, whether or not to treat “back pay” as wages; and their expert judgment is entitled, as we have said, to great weight.22 -¡The very fact *369that judicial review has been accorded, however, makes evident that such decisions are only conclusive as to properly supported findings of fact. Both Hearst Publications, p. 131, and Gray v. Powell, p. 411, advert to the limitations of administrative interpretations. Administrative determinations must have a basis in law and must be within the granted authority. Administration, when it interprets a statute so as to make it apply to particular circumstances, acts as a delegate to the legislative power. Congress might have declared that “back pay” awards under the Labor Act should or should not be treated as wages. Congress might have delegated to the Social Security Board to determine what compensation paid by employers to employees should be treated as wages. Except as such interpretive power may be included in the agencies’ administrative functions, Congress did neither. An agency may not finally decide the limits of its statutory power. That is a judicial function.23 Congress used a well understood word — “wages”— to indicate the receipts which were to govern taxes and benefits under the Social Security Act. There may be borderline payments to employees on which courts would follow administrative determination as to whether such payments were or were not wages under the act.

We conclude, however, that the Board’s interpretation of this statute to exclude back pay goes beyond the boundaries of administrative routine and the statutory limits. This is a ruling which excludes from the ambit *370of the Sócial Security Act payments which we think were included by Congress. It is beyond the permissible limits of administrative interpretation.

Petitioner further questions the validity of the decision of the circuit court of appeals on the ground that it must be inferred from the opihion that the “back pay” must be allocated as wages by the Board to the “calendar quarters” of the year in which the money would have been earned, if the employee had not been wrongfully discharged. We think this inference is correct.24 This conclusion, petitioner argues, tends to show that “back pay” cannot be wages because the Amendments of 1939 use “quarters” as the basis for eligibility as well as the measure of benefits and require “wages” to be “paid” in certain “quarters.”25

If, as we have held above, “back pay” is to be treated as wages, we have no doubt that it should be allocated to the periods when the regular wages were not paid as usual. Admittedly there are accounting difficulties which the Board will be called upon to solve but we do not believe they are insuperable.26

Affirmed.