delivered the opinion of the Court.
Petitioner union (along with the International Brotherhood of Teamsters and a number of other affiliated local unions) executed a three-year collective bargaining agreement with California Trucking Associations, which represented a group of motor truck operators in California. The provisions of the contract relating to hiring of casual or temporary employees were as follows:
“Casual employees shall, wherever the Union maintains a dispatching service, be employed only on a seniority basis in the Industry whenever such senior employee^ are available. An available list with seniority status will be kept by the Unions, and employees requested will be dispatched upon call to any employer who is a party to this Agreement. Seniority rating of such employees shall begin with a minimum of three months service in the Industry, irrespective of whether such employee is or is not a member of the Union. .
“Discharge of any employee by any employer shall be grounds for removal of any employee from seniority status. No casual employee shall be employed by any employer who is a party to this Agreement in violation of seniority status if such employees are available and if the dispatching service for such employees is available. The employer shall first call the Union or the dispatching hall designated *669by the Union for such help. In the event the employer is notified that such help is not available, or in the event the employees called for do not appear for work at the time designated by the employer, the employer may hire from any other available source.” (Emphasis added.)
Accordingly the union maintained a hiring hall for casual employees. One Slater was a member of the union and had customarily used the hiring hall. But in August 1955 he obtained casual employment with an employer who was party to the hiring-hall agreement without being dispatched by the union. He worked until sometime in November of that year, when he was discharged by the employer on complaint of the union that he had not been referred through the hiring-hall arrangement.
Slater made charges against the union and the employer. Though, as plain from the terms of the contract, there was an express provision that employees would not be discriminated against because they were or were not union members, the Board found that the hiring-hall provision was unlawful per se and that the discharge of Slater on the union’s request constituted a violation by the employer of § 8 (a) (1) and § 8 (a) (3) and a violation by the union of § 8 (b)(2) and §8 (b)(1)(A) of the National Labor Relations Act, as amended by the Taft-Hartley Act, 61 Stat. 140-141, as amended, 29 U. S. C. § 158.1 The *670Board ordered, inter alia, that the company and the union cease giving any effect to the hiring-hall agreement; that they jointly and severally reimburse Slater for any loss sustained by him as a result of his discharge; and that they jointly and severally reimburse all casual employees for fees and dues paid by them to the union beginning six months prior to the date of the filing of the charge. 121 N. L. R. B. 1629.
The union petitioned the Court of Appeals for review of the Board’s action, and the Board made a cross-application for enforcement. That court set aside the portion of the order requiring a general reimbursement of dues and fees. By a divided vote it upheld the Board in ruling that the hiring-hall agreement was illegal per se. 107 U. S. App. D. C. 188, 275 F. 2d 646. Those rulings are here on certiorari, 363 U. S. 837, one on the petition of the union, the other on petition of .the Board.
Our decision in Carpenters Local 60 v. Labor Board, decided this day, ante, p. 651, is dispositive of the petition *671of the Board that asks us to direct enforcement of the order of reimbursement. The judgment of the Court of Appeals on that phase of the matter is affirmed.
The other aspect of the case goes back to the Board’s ruling in Mountain Pacific Chapter, 119 N. L. R. B. 883. That decision, rendered in 1958, departed from earlier rulings2 and held, Abe Murdock dissenting, that the hiring-hall agreement, despite the inclusion of a nondiscrimination clause, was illegal per se:
“Here the very grant of work at all depends solely upon union sponsorship, and it is reasonable to infer that the arrangement displays and enhances the Union’s power and control over the employment status. Here all that appears is unilateral union determination and subservient employer action with no aboveboard explanation as to the reason for it, and it is reasonable to infer that the Union will be guided in its concession by an eye towards winning compliance with a membership obligation or union fealty in some other respect. The Employers here have surrendered all hiring authority to the Union and have given advance notice via the established hiring hall to the world at large that the Union is arbitrary master and is contractually guaranteed to remain so. From the final authority over hiring vested in the Respondent Union by the three AGC chapters, the inference of encouragement of union membership is inescapable.” Id., 896.
The Board went on to say that a hiring-hall arrangement to be lawful must contain protective provisions. Its views were stated as follows:
“We believe, however, that the inherent and unlawful encouragement of union membership that stems from unfettered union control over the hiring process *672would be negated, and we would find an agreement to be nondiscriminatory on its face, only if the agreement explicitly provided that:
“(1) Selection of applicants for referral to jobs shall be on a nondiscriminatory basis and shall not be based on, or in any way affected by, union membership, bylaws, rules, regulations, constitutional provisions, or any other aspect or obligation of union membership, policies, or requirements.
“(2) The employer retains the right to reject any job applicant referred by the union.
“(3) The parties to the agreement post in places where notices to employees and applicants for employment are customarily posted, all provisions relating to the functioning of the hiring arrangement, including the safeguards that we deem essential to the legality of an exclusive hiring agreement.” Id., 897.
The Board recognizes that the hiring hall came into being “to eliminate wasteful, time-consuming, and repetitive scouting for jobs by individual workmen and haphazard uneconomical searches by employers.” Id., 896, n. 8. The hiring hall at times has been a useful adjunct to the closed shop.3 But Congress may have thought that it need not serve that cause, that in fact it has served well both labor and management — particularly in the maritime field and in the building and construction industry.4 In the latter the contractor who frequently is a stranger to the area where the work is done requires a “central source” for his employment needs; 5 and a man *673looking for a job finds in the hiring hall “at least a minimum guarantee of continued employment.” 6
Congress has not outlawed the hiring hall, though it has outlawed the closed shop except within the limits prescribed in the provisos to § 8 (a) (3)..7 Senator Taft made clear his views that hiring halls are useful, that they are not illegal per se, that unions should be able to operate them so long as they are not used to create a closed shop:
“In order to make clear the real intention of Congress, it should be clearly stated that the hiring hall is not necessarily illegal. The employer should be able to make a contract with the union as an employment agency. The union frequently is the best employment agency. The employer should be able *674to give notice of vacancies, and in the normal course of events to accept men sent to him by the hiring hall. He should not be able to bind himself, however, to reject nonunion men if they apply to him; nor should he be able to contract to accept men on a rotary-hiring basis. . . .
“. . . The National Labor Relations Board and the courts did not find hiring halls as such illegal, but merely certain practices under them. The Board and the court found that the manner in which the hiring halls operated created in effect a closed shop in violation of the law. Neither the law nor these decisions forbid hiring halls, even hiring halls operated by the unions as long as they are not so operated as to create a closed shop with all of the abuses possible under such an arrangement, including discrimination against employees, prospective employees, members of union minority groups, and operation of a closed union.” S. Rep. No. 1827,81st Cong., 2d Sess., pp. 13, 14.
There being no express ban of hiring halls in any provisions of the Act, those who add one, whether it be the Board or the courts, engage in a legislative act. The Act deals with discrimination either by the employers or unions that encourages or discourages union membership.8 As respects § 8 (a) (3) we said in Radio Officers v. Labor Board, 347 U. S. 17, 42-43:
“The language of § 8 (a) (3) is not ambiguous. The unfair labor practice is for an employer to encourage or discourage membership by means of discrimination. Thus this section does not outlaw all encouragement or discouragement of membership in labor organizations; only such as is accomplished *675by discrimination is prohibited. Nor does this section outlaw discrimination in employment as such; only such discrimination as encourages or discourages membership in a labor organization is proscribed.”
It is the “true purpose” or “real motive” in hiring or firing that constitutes the test. Id., 43. Some conduct may by its very nature contain the implications of the required intent; the natural foreseeable consequences of certain action may warrant the inference. Id., 45. And see Republic Aviation Corp. v. Labor Board, 324 U. S. 793. The existence of discrimination may at times be inferred by the Board, for “it is permissible to draw on experience in factual inquiries.” Radio Officers v. Labor Board, supra, 49.
But surely discrimination cannot be inferred from the face of the instrument when the instrument specifically provides that there will be no discrimination against “casual employees” because of the presence or absence of union membership. The only complaint in the case was by Slater, a union member, who sought to circumvent the hiring-hall agreement. When an employer and the union enforce the agreement against union members, we cannot say without more that either indulges in the kind of discrimination to which the Act is addressed.
It may be that the very existence of the hiring hall encourages union membership. We may assume that it does. The very existence of the union has the same influence. When a union engages in collective bargaining and obtains increased wages and improved working conditions, its prestige doubtless rises and, one may assume, more workers are drawn to it. When a union negotiates collective bargaining agreements that include arbitration clauses and supervises the functioning of those provisions so as to get equitable adjustments of grievances, union membership may also be encouraged. The truth is that the union is a service agency that probably encourages *676membership whenever it does its job well. But, as we said in Radio Officers v. Labor Board, supra, the only encouragement or discouragement of union membership banned by the Act is that which is “accomplished by discrimination.” P. 43.
Nothing is inferable from the present hiring-hall provision except that employer and union alike sought to route “casual employees” through the union hiring hall and required a union member who circumvented it to adhere to it.
It may be that hiring halls need more regulation than the Act presently affords. As we have seen, the Act aims at every practice, act, source or institution which in fact is used to encourage and discourage union membership by discrimination in regard to hire or tenure, term or condition of employment. Perhaps the conditions which the Board attaches to hiring-hall arrangements will in time appeal to the Congress. Yet, where Congress has adopted a selective system for dealing with evils, the Board is confined to that system. Labor Board v. Drivers Local Union, 362 U. S. 274, 284-290. Where, as here, Congress has aimed its sanctions only at specific discriminatory practices, the Board cannot go farther and establish a broader, more pervasive regulatory scheme.
The present agreement for a union hiring hall has a protective clause in it, as we have said; and there is no evidence that it was in fact used unlawfully. We cannot assume that a union conducts its operations in violation of law or that the parties to this contract did not intend to adhere to its express language. Yet we would have to make those, assumptions to agree with the Board that it is reasonable to infer the union will act discriminatorily.
Moreover, the hiring hall, under the law as it stands, is a matter of negotiation between the parties. The Board has no power to compel directly or indirectly that the hiring hall be included or excluded in collective agree*677ments. Cf. Labor Board v. American Ins. Co., 343 U. S. 395, 404. Its power, so far as here relevant, is restricted to the elimination of discrimination. Since the present agreement contains such a prohibition, the Board is confined to determining whether discrimination has in fact been practiced. If hiring halls are to be subjected to regulation that is less selective and more pervasive, Congress not the Board is the agency to do it.
Affirmed in part and reversed in part.
Mr. Justice Frankfurter took no part in the consideration or decision of this case.Section 8 provides in relevant part:
“(a) It shall be an unfair labor practice for an employer—
“(1) to interfere with, restrain, or coerce employees in the exercise of the rights guaranteed in section 7;
“(3) by discrimination in regard to hire or tenure of employment or any term or condition of employment to encourage or discourage membership in any labor organization . . .
*670“(b) It shall be an unfair labor practice for a labor organization or its agents—
“(1) to restrain or coerce (A) employees in the exercise of the rights guaranteed in section 7 . . .
“(2) to cause or attempt to cause an employer to discriminate against an employee in violation of subsection (a) (3) or to discriminate against an employee with respect to whom membership in such organization has been denied or terminated on some ground other than his failure to tender the periodic dues and the initiation fees uniformly required as a condition of acquiring or retaining membership
Section 7 provides:
“Employees shall have the right to self-organization, to form, join, or assist labor organizations, to bargain collectively through representatives of their own choosing, and to engage in other concerted activities for the purpose of collective bargaining or other mutual aid or protection, and shall also have the right to refrain from any or all of such activities except to the extent that such right may be affected by an agreement requiring membership in a labor organization as a condition of employment as authorized in section 8 (a) (3)
See Hunkin-Conkey Constr. Co., 95 N. L. R. B. 433, 435.
Fenton, Union Hiring Halls Under the Taft-Hartley Act, 9 Lab. L. Jour. 505, 506 (1958).
Cf. id., at 507. For expression of such view see S. Rep. No. 1827, 81st Cong., 2d Sess., pp. 4-8; Goldberg, The Maritime Story (1958), pp. 277-282.
Fenton, op. cit., supra, note 3, at 507.
Id., at 507.
Those provisos read:
“Provided, That nothing in this Act, or in any other statute of the United States, shall preclude an employer from making an agreement with a labor organization (not established, maintained, or assisted by any action defined in section 8 (a) of this Act as an unfair labor practice) to require as a condition of employment membership therein on or after the thirtieth day following the beginning of such employment or the effective date of such agreement, whichever is the later, (i) if' such labor organization is the representative of the employees as provided in section 9 (a), in the appropriate eollective-bargaining unit covered by such agreement when made; and (ii) unless following an election held as provided in section 9 (e) within one year preceding the effective date of such agreement, the Board shall have certified that at least a majority of the employees eligible to vote in such election have voted to rescind the authority of such labor organization to make such an agreement: Provided further, That no employer shall justify any discrimination against an employee for nonmember-ship in a labor organization (A) if he has reasonable grounds for believing that such membership was not available to the employee on the same terms and conditions generally applicable to other members, or (B) if he has reasonable grounds for believing that membership was denied or terminated for reasons other than the failure of the employee to tender the periodic dues and the initiation fees uniformly required as a conditon of acquiring or retaining membership
See §§ 7 and 8, supra, note 1.