delivered the opinion of the Court.

The National Labor Relations Board, acting pursuant to § 9 (c) of the National Labor Relations Act, as *271amended, 61 Stat. 144,1 29 U. S. C. § 159 (c), conducted an election by secret ballot among the production and maintenance employees of respondent at the request of the Mechanics Educational Society of America (hereafter Union). Under the Act2 the Union, if it wins the election, becomes “the exclusive representative of all the employees” in that particular unit for purposes of collective bargaining. The Union won the election by a vote of 22-20.

Respondent filed objections to the election, but after an evidentiary hearing, a hearing officer found against respondent and the Board certified the Union as the representative of the employees in that unit. Respondent, however, refused to bargain. The Union thereupon filed *272an unfair labor practice charge with the General Counsel, who issued a complaint alleging that respondent had violated §§ 8 (a)(1) and (5) of the Act.3 The Board sustained the allegations and ordered respondent to bargain with the Union. 194 N. L. R. B. 298. The Court of Appeals denied enforcement of the order. 470 F. 2d 305. We granted the petition for certiorari, 411 U. S. 964, there apparently being a conflict between this decision in the Sixth Circuit and a decision in the Eighth Circuit, NLRB v. DIT-MCO, Inc., 428 F. 2d 775, and also with one in the Ninth Circuit, NLRB v. G. K. Turner Associates, 457 F. 2d 484. We affirm.

It appeared that prior to the election, “recognition slips” were circulated among employees. An employee who signed the slip before the election4 became a mem*273ber of the Union and would not have to pay what at times was called an “initiation fee” and at times a “fine.” If the Union was voted in, those who had not signed a recognition slip would have to pay.

*274The actual solicitation of signatures on the “recognition slips” was not done by Union officials. Union officials, however, explained to employees at meetings that those who signed the slips would not be required to pay an initiation fee, while those who did not would have to pay. Those officials also picked out some five employees to do the soliciting and authorized them to explain the Union’s initiation-fee policy. Those solicited were told that there would be no initiation fee charged those who signed the slip before the election. Under the bylaws of the Union, an initiation fee apparently was not to be higher than $10; but the employees who testified at the hearing (1) did not know how large the fee would be and (2) said that their understanding was that the fee was a “fine” or “assessment.”

*275One employee, Donald Bridgeman, testified that he signed the slip to avoid paying the “fine” if the Union won. He got the message directly from an employee picked by the Union to solicit signatures on the “slips.” So did Thomas Rice, another employee.

The Board originally took the position that pre-election solicitation of memberships by a union with a promise to waive the initiation fee of the union was not consistent with a fair and free choice of bargaining representatives. Lobue Bros., 109 N. L. R. B. 1182. Later in DIT-MCO, Inc., 163 N. L. R. B. 1019, the Board explained its changed position as follows:

“We shall assume, arguendo, that employees who sign cards when offered a waiver of initiation fees do so solely because no cost is thus involved; that they in fact do not at that point really want the union to be their bargaining representative. The error of the Lobue premise can be readily seen upon a review of the consequences of such employees casting votes for or against union representation. Initially, it is obvious that employees who have received or been promised free memberships will not be required to pay an initiation fee, whatever the outcome of the vote. If the union wins the election, there is by postulate no obligation; and if the union loses, there is still no obligation, because compulsion to pay an initiation fee arises under the Act only when a union becomes the employees’ representative and negotiates a valid union-security agreement. Thus, whatever kindly feeling toward the union may be generated by the cost-reduction offer, when consideration is given only to the question of initiation fees, it is completely illogical to characterize as improper inducement or coercion to *276vote 'Yes’ a waiver of something that can be avoided simply by voting 'No.’

“The illogic of Lobue does not become any more logical when other consequences of a vote for representation are considered. Thus, employees know that if a majority vote for the union, it will be their exclusive representative, and, provided a valid union-security provision is negotiated, they will be obliged to pay dues as a condition of employment. Thus, viewed solely as a financial matter, a 'no’ vote will help to avoid any subsequent obligations, a 'yes’ may well help to incur such obligations. In these circumstances, an employee who did not want the union to represent him would hardly be likely to vote for the union just because there would be no initial cost involved in obtaining membership. Since an election resulting in the union’s defeat would entail not only no initial cost, but also insure that no dues would have to be paid as a condition of employment, the financial inducement, if a factor at all, would be in the direction of a vote against the union, rather than for it.” Id., at 1021-1022.

We are asked to respect the expertise of the Board on this issue, giving it leeway to alter or modify its policy in light of its ongoing experience with the problem. The difficulty is not in that principle but with the standards to govern the conduct of elections under §9 (c)(1)(A). We said in NLRB v. Tower Co., 329 U. S. 324, 330, that the duty of the Board was to establish “the procedure and safeguards necessary to insure the fair and free choice of bargaining representatives by employees.”

It is, of course, true as we said in NLRB v. Wyman-Gordon Co., 394 U. S. 759, 767, that “Congress granted the Board a wide discretion to ensure the fair and *277free choice of bargaining representatives.” See also NLRB v. Waterman S. S. Co., 309 U. S. 206, 226. But in this case two opposed groups are in contention: one composed of those who want a union and the other, of those who prefer not to have one. The Board in its DIT-MCO opinion says “it is completely illogical to characterize as improper inducement or coercion” a waiver of initiation fees for those who vote “yes” when the whole problem can be avoided by voting “no.” 163 N. L. R. B., at 1021-1022. But the Board’s analysis ignores the realities of the situation.

Whatever his true intentions, an employee who signs a recognition slip prior to an election is indicating to other workers that he supports the union. His outward manifestation of support must often serve as a useful campaign tool in the union’s hands to convince other employees to vote for the union, if only because many employees respect their coworkers’ views on the unionization issue. By permitting the union to offer to waive an initiation fee for those employees signing a recognition slip prior to the election, the Board allows the union to buy endorsements and paint a false portrait of employee support during its election campaign.

That influence may well have been felt here for, as noted,5 there were 28 who signed up with the Union before the election petition was filed with the Board and either seven or eight more who signed up before the election. We do not believe that the statutory policy of fair elections prescribed in the Tower case permits endorsements, whether for or against the union, to be bought and sold in this fashion.

In addition, while it is correct that the employee who signs a recognition slip is not legally bound to vote for the union and has not promised to do so in any formal *278sense, certainly there may be some employees who would feel obliged to carry through on their stated intention to support the union. And on the facts of this case, the change of just one vote would have resulted in a 21-21 election rather than a 22-20 election.

Any procedure requiring a “fair” election must honor the right of those who oppose a union as well as those who favor it. The Act is wholly neutral when it comes to that basic choice. By § 7 of the Act employees have the right not only to “form, join, or assist” unions but also the right “to refrain from any or all of such activities.” 29 U. S. C. § 157. An employer who promises to increase the fringe benefits by $10 for each employee who votes against the union, if the union loses the election, would cross the forbidden line under our decisions. See NLRB v. Exchange Parts Co., 375 U. S. 405. The right of employees to “form, join, or assist” labor unions guaranteed by § 7 has an express sanction in § 8 (a)(1) which makes it an unfair labor practice for an employer “to interfere with, restrain, or coerce employees ” in the exercise of those rights. 29 U. S. C. §§ 157, 158 (a)(1). Such interference is an unfair labor practice as we held in NLRB v. Exchange Parts Co., supra. But, as already noted, § 7 guarantees the right of employees “to refrain from any or all of such activities.”

Congress has also listed in § 8 (b) of the Act “unfair” labor practices of unions. 29 U. S. C. § 158 (b). There is no explicit provision which makes “interference” by a union with the right of an employee to “refrain” from union activities an unfair labor practice.

Section 8 (c), however, provides:

“The expressing of any views, argument, or opinion, or the dissemination thereof, whether in written, printed, graphic, or visual form, shall not constitute or be evidence of an unfair labor practice under any of the provisions of this subchapter, if such expression contains no threat *279of reprisal or force or promise of benefit.” 29 U. S. C. § 158 (c) (emphasis added).

Whether it would be an “unfair” labor practice for a union to promise a special benefit to those who sign up for a union seems not to have been squarely resolved.6 The right of a free choice is, however, inherent in the principles reflected in § 9 (c)(1)(A).

When the dissent says that “[t]he special inducement is to sign the card, not to vote for the union” and that treating the two choices as one is untenable, it overlooks cases like NLRB v. Gissel Packing Co., 395 U. S. *280575. There we held that the gathering of authorization cards from a majority of the employees in the bargaining unit may entitle the union to represent the employees for collective-bargaining purposes, even though there has been and will be no election, id., at 582-583, and that rejection of that authorization by the employer is an unfair labor practice. Where the solicitation of cards is represented as being solely for the purpose of obtaining an election, a contrary result is indicated. Id., at 584, 606. Thus the solicitation of authorization cards may serve one of two ends. Of course, when an election is contemplated, an employee does not become a member of the union merely by signing a card. But prior to the election if the union receives overwhelming support, the pro-union group may decide to treat the union authorization cards as authorizing it to conduct collective bargaining without an election. The latent potential of that alternative use of authorization cards cautions us to treat the solicitation of authorization cards in exchange for consideration of fringe benefits granted by the union as a, separate step protected by the same kind of moral standard that governs elections themselves.

The Board in its supervision of union elections may not sanction procedures that east their weight for the choice of a union and against a nonunion shop or for a nonunion shop and against a union.

In the Exchange Parts case we said that, although the benefits granted by the employer were permanent and unconditional, employees were “not likely to miss the inference that the source of benefits now conferred is also the source from which future benefits must flow and which may dry up if it is not obliged.” 375 U. S., at 409. If we respect, as we must, the statutory right of employees to resist efforts to unionize a plant, we cannot assume that unions exercising powers are wholly benign towards their antagonists whether they be nonunion *281protagonists or the employer. The failure to sign a recognition slip may well seem ominous to nonunionists who fear that if they do not sign they will face a wrathful union regime, should the union win. That influence may well have had a decisive impact in this case where a change of one vote would have changed the result.

Affirmed.

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

The report of the Hearing Officer, filed in response to the Company’s objections to the election, reveals that prior to the filing of the representation petition, a union organizer had told employees that, if the Union won the election, they would be subject to an initiation fee or “fine” if they did not sign an authorization card. The Union was then engaged in securing the necessary 30% showing of union support which would entitle it to hold an election under the Labor Board’s rules. 29 CFB, §§ 101.17, 101.18 (1973). The officer concluded that there was “insufficient evidence . . . that a threat of a 'fine’ occurred either before or after the filing date of the petition.” In any event, he also concluded that conduct occurring before the filing of an election petition was not ground for setting aside the election since “[w]hether or not a sufficient valid showing of interest was obtained, constitutes a matter for administrative determination.” Cf. Goodyear Tire & Rubber Co., 138 N. L. R. B. 453 (1962).1

After the representation petition was filed and the election campaign proper commenced, the Union’s Sec*282retary-Treasurer, Alfred Smith, addressed a group of about 20 employees at an organization meeting. In response to a question about the initiation fee, Smith indicated that there was “a small fee” which would be waived for all employees who signed cards prior to the election.2 The fee was, in fact, $10. Qualification for fee waiver was obtained by signing membership cards, but the testimony indicated that no one incurred any obligation to the Union until and unless the Union became the bargaining agent and a collective contract was signed. The Hearing Officer found “no evidence, nor any contention, that the Union misrepresented to employees that they would have to become members immediately upon the certification of the union as bargaining agent.”

On this record, the Board, obviously relying on its decision in DIT-MCO, Inc., 163 N. L. R. B. 1019 (1967), enforced, 428 F. 2d 775 (CA8 1970), which overruled its prior decision in Lobue Bros., 109 N. L. R. B. 1182 (1954), ordered the employer to bargain with the Union. 194 N. L. R. B. 298 (1971). The Sixth Circuit denied enforcement of the order, 470 F. 2d 305 (1972), and the majority now affirms that judgment.

Because in my view the Labor Board has “a wide degree of discretion in establishing the procedure and safeguards necessary to insure the fair and free choice of bargaining representatives by employees,” NLRB v. Tower Co., 329 U. S. 324, 330 (1946), and because I am unpersuaded that the waiver of initiation fees in this case is so clearly coercive within § 7 of the National Labor Relations Act that the Board has abused its discretion in finding otherwise, I respectfully dissent.

*283I

It is well established that an “unconditional” offer to waive initiation fees, where the waiver offer is left open for some period of time after the election, is not coercive and does not constitute an unfair labor practice. The Sixth Circuit itself has so held, NLRB v. Gafner Automotive & Machine, Inc., 400 F. 2d 10 (1968), and other courts of appeals have reached the same result. Amalgamated Clothing Workers v. NLRB, 345 F. 2d 264 (CA2 1965); NLRB v. Crest Leather Mfg. Corp., 414 F. 2d 421 (CA5 1969). The existence of the initiation fee is created by the union 'and represents .a self-imposed barrier to entry.3 There is no evidence that the fee is normally imposed for the sole purpose of removing it during a labor campaign. A different case might be put if the union purported to remove a nonexistent fee or artificially inflated the fee so as to misrepresent the benefit tendered by its removal. See NLRB v. Corbea, Perez & Morell, 328 F. 2d 679 (CA1 1964). Similarly, it is established that the union can promise employees to obtain wage increases or other benefits if it is elected as a bargaining representative. Wilson Athletic Goods Mjg. Co. v. NLRB, 164 F. 2d 637 (CA7 1947).

It must be obvious that these waivers of fees are a form of economic inducement, as the opinion for the Court employs that term. Undoubtedly an offer to reduce the cost of joining the union makes the union a *284more attractive possibility and may influence an employee to vote for the union, though one would assume, in view of the other costs and benefits at stake, that this consideration will be marginal. Similarly, if the union represents to the employees that it will attempt to secure higher wages, an employee’s calculations of costs and benefits will be altered, but in that instance the union is merely stating the obvious; indeed, the promise of higher wages is the primary rationale for the existence of the union. In any event, these forms of inducement are valid.

In the instant case, an offer which by its terms expires with the conclusion of the election is also a form of economic inducement. But insofar as the offer might affect the calculation of costs and benefits of joining the union, its effect is the same as an offer which does not expire until some time after the election. The inability to distinguish between these two situations, at least where small fees are involved and where the sole source of concern is pure financial inducement, led the Board to conclude in DIT-MCO that “an employee who did not want the union to represent him would hardly be likely to vote for the union just because there would be no initial cost involved in obtaining membership.” 163 N. L. R. B., at 1022.

The majority places heavy reliance on the supposed analogy between the waiver of fees in this case and an actual increase in benefits made by an employer during the course of an election campaign. NLRB v. Exchange Parts Co., 375 U. S. 405 (1964). There the employer increased vacation-pay benefits during the course of the campaign. The Court agreed with the Board that this was coercive activity on the part of the employer, and accordingly reversed the Court of Appeals, and ordered enforcement of the Board’s order. It was stated that *285"[t]he danger inherent in well-timed increases in benefits is the suggestion of a fist inside the velvet glove.” Id., at 409. A number of important differences exist between that case and the instant one. First, the employer actually gave his employees substantial increased benefits, whereas here the benefit is only contingent and small; the union glove is not very velvet. Secondly, in the union context, the fist is missing. When the employer increased benefits, the threat was made “that the source of benefits now conferred is also the source from which future benefits must flow and which may dry up if it is not obliged.” Ibid. The Union, on the other hand, since it was not the representative of the employees, and would not be if it were unsuccessful in the election, could not make the same threat by offering a benefit which it would take away if it lost the election. A union can only make its own victory more desirable in the minds of the employees.4

II

If pure economic inducement in the form of lowering anticipated costs of joining the union is not to be con*286sidered coercive, one must focus on the special dangers, if any, presented by the conditional offer, an analysis not undertaken by the majority. It has been proposed that the conditional offer is specially to be proscribed because of the interjection of a new consideration into the voting choice of an employee: how probable it is that the union will win or lose the election. NLRB v. Gafner Automotive & Machine, Inc., 400 F. 2d, at 13 (Phillips, J., concurring); Amalgamated Clothing Workers v. NLRB, 345 F. 2d, at 268 (Friendly, J., concurring). The argument might be that an employee who estimates that the costs of joining the union exceed the benefits, even taking into account the reduced initiation fees available by signing a card, will still sign the card, as a hedge, because of his prediction that the union will win the election.5 A statement of the theory carries with it its own disproof. The special inducement is to sign the card, not to vote for the union. The majority decision collapses these two choices into one, and is thus untenable. The majority assumes, contrary to fact, that the employee has joined the Union by signing the authorization card. This is only true, however, if the Union wins the election and signs a collective contract, and the employee can still seek to prevent that outcome by cast*287ing his vote against the Union in a secret ballot. The testimony was clear that if the Union loses the election, the employee who signs the card incurs no obligation to the Union. The expressed preference in the National Labor Relations Act for secret ballot elections assumes that voters may act differently in private than in public, and ordinarily guarantees to employees the ability to make a secret choice. It is, therefore, important to highlight the fact that the Board in DIT-MCO assumed, arguendo, “that employees who sign cards when offered a waiver of initiation fees do so solely because no cost is thus involved; that they in fact do not at that point really want the union to be their bargaining representative.” 163 N. L. R. B., at 1021.

There is no need to consider here, as does the majority, whether the Union could achieve recognition on the basis of authorization cards secured, in part, by an offer of fee waiver. Of course, a card majority cannot serve as a basis for a § 8 (a) (5) bargaining order under NLRB v. Gissel Packing Co., 395 U. S. 575, 614-616 (1969), unless the employer has committed serious unfair labor practices. It may be that even given a serious unfair labor practice on the part of the employer, these cards could not serve as a basis for recognition. In this case, however, the Board’s bargaining order was based on the vote of a secret ballot election, and the Court must supply the connective between the decision to sign a card and the decision to vote for the Union.6 *288This connective can only be supplied by some rather speculative counter-rational psychological assumptions, i. e., that a person who signs the card will vote for the union.7 The Board assumes that such is not the case, and I am not prepared to upset the Board’s judgment on this matter.8 The majority opinion stresses the fact that the margin of Union victory was only two *289votes, and thus suggests that the “psychological connective” may explain the outcome indicating that it “may well have had a decisive impact” (emphasis added). But there is no evidence to this effect, and definitions of unfair practices which become a function of the outcome of an election are subject to severe problems of administration. The Board, in my judgment, is entitled to regulate elections on standard theories of coercion.

Ill

Since the case for coercion arising out of the conditional offer is speculative, and since the alteration of the calculus of costs and benefits is marginal where a small fee is involved, the issue here resolves into the proper allocation of institutional responsibility between an administrative agency and a reviewing court. The Board, upon reflection and study, has concluded that the conditional offer is not coercive within the meaning of § 7. This represented a basic change in policy but “one of the signal attributes of the administrative process is flexibility in reconsidering and reforming of policy.” City of Chicago v. FPC, 128 U. S. App. D. C. 107, 115, 385 F. 2d 629, 637 (1967). Such revisions are especially likely in the regulation of labor elections, due to the substantial problems in deciding what is likely to interfere with employee free choice. See Bok, The Regulation of Campaign Tactics in Representation Elections under the National Labor Relations Act, 78 Harv. L. Rev. 38, 44-45 (1964).

While the invocation of agency expertise is not talis-manic, see Radio Corp. v. United States, 341 U. S. 412, 421 (1951) (Frankfurter, J., dubitante), and while the decision of the Board must be supported by substantial evidence, Universal Camera Corp. v. NLRB, 340 U. S. 474 (1951), one cannot ask the agency to do the impossible. When choosing between alternative contentions *290of coercion, the agency must make judgments based on available knowledge. This is a difficult task and accounts in part for the decision of Congress to entrust the Board “with a wide degree of discretion in establishing the procedure and safeguards necessary to insure the fair and free choice of bargaining representatives by employees.” NLRB v. Tower Co., 329 U. S., at 330. Recognition of this discretion has been a recurrent theme in this Court's review of Board decisions. NLRB v. Waterman S. S. Co., 309 U. S. 206, 226 (1940); NLRB v. Wyman-Gordon Co., 394 U. S. 759, 767 (1969). In other contexts, the Board has had to perform the “far more delicate task ... of weighing the interests of employees in concerted activity against the interest of the employer in operating his business in a particular manner . . . .” NLRB v. Erie Resistor Corp., 373 U. S. 221, 229 (1963); American Ship Bldg. Co. v. NLRB, 380 U. S. 300, 312 (1965). There is certainly a conflicting interest between the union's right to make itself attractive to employees without misrepresentation and the employee's unfettered choice to vote for or against the union. I think it is rational for the Board to conclude on the basis of the facts presented that the decision of the Union to waive small fees was not coercive within the meaning of § 7. I, therefore, respectfully dissent.