delivered the opinion of the Court.
In these cases an employer insisted that its collective-bargaining contract with certain of its employees include: (1) a “ballot” clause calling for a pre-strike secret vote of those employees (union and nonunion) as to the employer’s last offer, and (2) a “recognition” clause which excluded, as a party to the contract, the International Union which had been certified by the National Labor Relations Board as the employees’ exclusive bargaining *344agent, and substituted for it the agent’s uncertified local affiliate. The Board held that the employer’s insistence upon either of such clauses amounted to a refusal to bargain, in violation of § 8 (a) (5) of the National Labor Relations Act, as amended.1 The issue turns on whether either of these clauses comes within the scope of mandatory collective bargaining as defined in § 8 (d) of the Act.2 For the reasons hereafter stated, we agree with the Board that neither clause comes within that definition. Therefore, we sustain the Board’s order directing the employer to cease insisting upon either clause as a condition precedent to accepting any collective-bargaining contract.
Late in 1952, the International Union, United Automobile, Aircraft and Agricultural Implement Workers of America, CIO (here called International) was certified by the Board to the Wooster (Ohio) Division of the Borg-Warner Corporation (here called the company) as the elected representative of an appropriate unit of the company’s employees. Shortly thereafter, International chartered Local No. 1239, UAW-CIO (here called the Local). Together the unions presented the company with a comprehensive collective-bargaining agreement. In the “recognition” clause, the unions described themselves as both the “International Union, *345United Automobile, Aircraft and Agricultural Implement Workers of America and its Local Union No. 1239, U. A. W.-C. 1.0.”
The company submitted a counterproposal which recognized as the sole representative of the employees “Local Union 1239, affiliated with the International Union, United Automobile, Aircraft and Agricultural Implement Workers of America (UAW-CIO).” The unions’ negotiators objected because such a clause disregarded the Board’s certification of International as the employees’ representative. The negotiators declared that the employees would accept no agreement which excluded International as a party.
The company’s counterproposal also contained the “ballot” clause, quoted in full in the margin.3 In sum*346mary, this clause provided that, as to all nonarbitrable issues (which eventually included modification, amendment or termination of the contract), there would be a 30-day negotiation period after which, before the union could strike, there would have to be a secret ballot taken among all employees in the unit (union and nonunion) on the company’s last offer. In the event a majority of the employees rejected the company’s last offer, the company would have an opportunity, within 72 hours, of making a new proposal and having a vote on it prior to any strike. The unions’ negotiators announced they would not accept this clause “under any conditions.”
From the time that the company first proposed these clauses, the employees’ representatives thus made it clear *347that each was wholly unacceptable. The company’s representatives made it equally clear that no agreement would be entered into by it unless the agreement contained both clauses. In view of this impasse, there was little further discussion of the clauses, although the parties continued to bargain as to other matters. The company submitted a “package” proposal covering economic issues but made the offer contingent upon the satisfactory settlement of “all other issues . . . .” The “package” included both of the controversial clauses. On March 15, 1953, the unions rejected that proposal and the membership voted to strike on March 20 unless a settlement were reached by then. None was reached and the unions struck. Negotiations, nevertheless, continued. On April 21, the unions asked the company whether the latter would withdraw its demand for the “ballot” and “recognition” clauses if the unions accepted all other pending requirements of the company. The company declined and again insisted upon acceptance of its “package,” including both clauses. Finally, on May 5, the Local, upon the recommendation of International, gave in and entered into an agreement containing both controversial clauses.
In the meantime, International had filed charges with the Board claiming that the company, by the above conduct, was guilty of an unfair labor practice within the meaning of § 8 (a) (5) of the Act. The trial examiner found no bad faith on either side. However, he found that the company had made it a condition precedent to its acceptance of any agreement that the agreement include both the “ballot” and the “recognition” clauses. For that reason, he recommended that the company be found guilty of a per se unfair labor practice in violation of §8 (a)(5). He reasoned that, because each of the controversial clauses was outside of the scope of mandatory bargaining as defined in § 8 (d) of the Act, the com*348pany’s insistence upon them, against the permissible opposition of the unions, amounted to a refusal to bargain as to the mandatory subjects of collective bargaining. The Board, with two members dissenting, adopted the recommendations of the examiner. 113 N. L. R. B. 1288, 1298. In response to the Board’s petition to enforce its order, the Court of Appeals set aside that portion of the order relating to the “ballot” clause, but upheld the Board’s order as to the “recognition” clause. 236 F. 2d 898.
Because of the importance of the issues and because of alleged conflicts among the Courts of Appeals,4 we granted the Board’s petition for certiorari in No. 53, relating to the “ballot” clause, and the company’s cross-petition in No. 78, relating to the “recognition” clause. 353 U. S. 907.
We turn first to the relevant provisions of the statute. Section 8 (a) (5) makes it an unfair labor practice for an employer “to refuse to bargain collectively with the representatives of his employees . . . .” 5 Section 8 (d) defines collective bargaining as follows:
“(d) For the purposes of this section, to bargain collectively is the performance of the mutual obligation of the employer and the representative of the employees to meet at reasonable times and confer in good faith with respect to wages, hours, and other terms and conditions of employment, or the negotiation of an agreement, or any question arising thereunder, and the execution of a written contract incorporating any agreement reached if requested by either party, but such obligation does not compel *349either party to agree to a proposal or require the making of a concession 61 Stat. 142, 29 U. S. C. § 158 (d).
Read together, these provisions establish the obligation of the employer and the representative of its employees to bargain with each other in good faith with respect to “wages, hours, and other terms and conditions of employment . . . The duty is limited to those subjects, and within that area neither party is legally obligated to yield. Labor Board v. American Insurance Co., 343 U. S. 395. As to other matters, however, each party is free to bargain or not to bargain, and to agree or not to agree.
The company’s good faith has met the requirements of the statute as to the subjects of mandatory bargaining. But that good faith does not license the employer to refuse to enter into agreements on the ground that they do not include some proposal which is not a mandatory subject of bargaining. We agree with the Board that such conduct is, in substance, a refusal to bargain about the subjects that are within the scope of mandatory bargaining. This does not mean that bargaining is to be confined to the statutory subjects. Each of the two controversial clauses is lawful in itself.6 Each would be enforceable if agreed to by the unions. But it does not follow that, because the company may propose these clauses, it can lawfully insist upon them as a condition to any agreement.
Since it is lawful to insist upon matters within the scope of mandatory bargaining and unlawful to insist upon matters without, the issue here is whether either the “ballot” or the “recognition” clause is a subject within the phrase “wages, hours, and other terms and conditions of employment” which defines mandatory bargaining. The “ballot” clause is not within that definition. It re*350lates only to the procedure to be followed by the employees among themselves before their representative may call a strike or refuse a final offer. It settles no term or condition of employment — it merely calls for an advisory vote of the employees. It is not a partial “no-strike” clause. A “no-strike” clause prohibits the employees from striking during the life of the contract. It regulates the relations between the employer and the employees. See Labor Board v. American Insurance Co., supra, at 408, n. 22. The “ballot” clause, on the other hand, deals only with relations between the employees and their unions. It substantially modifies the collective-bargaining system provided for in the statute by weakening the independence of the “representative” chosen by the employees. It enables the employer, in effect, to deal with its employees rather than with their statutory representative. Cf. Medo Photo Corp. v. Labor Board, 321 U. S. 678.
The “recognition” clause likewise does not come within the definition of mandatory bargaining. The statute requires the company to bargain with the certified representative of its employees. It is an evasion of that duty to insist that the certified agent not be a party to the collective-bargaining contract. The Act does not prohibit the voluntary addition of a party, but that does not authorize the employer to exclude the certified representative from the contract.
Accordingly, the judgment of the Court of Appeals in No. 53 is reversed and the cause remanded for disposition consistent with this opinion. In No. 78, the judgment is affirmed.
No. 53 — Reversed and remanded.
No. 78 — Affirmed.Mr. Justice Frankfurter
joins this opinion insofar as it holds that insistence by the company on the “recognition” clause, in conflict with the provisions of the Act *351requiring an employer to bargain with the representative of his employees, constituted an unfair labor practice. He agrees with the views of Mr. Justice Harlan regarding the “ballot” clause. The subject matter of that clause is not so clearly outside the reasonable range of industrial bargaining as to establish a refusal to bargain in good faith, and is not prohibited simply because not deemed to be within the rather vague scope of the obligatory provisions of § 8 (d).
“Sec. 8. (a) It shall be an unfair labor practice for an employer—
“(5) to refuse to bargain collectively with the representatives of his employees, subject to the provisions of section 9 (a).
“Sec. 9. (a) Representatives designated' or selected for the purposes of collective bargaining by the majority of the employees in a unit appropriate for such purposes, shall be the exclusive representatives of all the employees in such unit for the purposes of collective bargaining in respect to rates of pay, wages, hours of employment, or other conditions of employment . . . .” 61 Stat. 140, 141, 143, 29 U. S. C. §§158 (a)(5), 159 (a).
See § 8 (d) as set forth in the text of the opinion, infra, p. 348.
“5. RESPONSIBILITIES OF THE COMPANY AND THE UNION
“5.4 It is agreed by both the Company and the Union that it is their mutual intent to provide peaceful means for the settlement of all disputes that may arise between them. To assist both parties to carry out this intent in good faith, it is agreed that it is essential that three basic steps be taken with respect to each dispute, in order to permit the greatest opportunity for satisfactory settlement: such steps shall include (1) a clear definition of the issue or issues, officially made known to all employees in the bargaining unit; (2) a reasonable period of good faith bargaining on the issues as defined, after such issues have been made known to all employees in the bargaining unit; and (3) an opportunity for all employees in the bargaining unit to vote, by secret, impartially supervised, written ballot, on whether to accept or reject the Company’s last offer, and on any subsequent offers made.
“5.5 It is mutually agreed that the definition of issues referred to in Section 5.4 will include the proposals and counter-proposals of each party; that the reasonable period of good faith bargaining referred to in Section 5.4 shall be at least 30 days, with full discussion of the issue taking place during that period; and that the secret written ballot referred to in Section 5.4 shall be supervised by a representative of the United States Mediation and Conciliation Serv*346ice, or by some other party mutually agreed upon by the Company and the Union. The Company and the Union further agree that such a ballot shall be taken on Company premises, at reasonable and convenient times, and with proper safeguards, similar to those observed in NLRB elections, being taken to insure freedom of choice.and a fair election.
“5.6 It is further mutually agreed that if a majority of employees in the bargaining unit reject the Company’s last offer, and the Company makes a subsequent offer within 72 hours from the time the results of the election are known, another secret, impartially supervised written ballot will be taken within the following 72 hours.
“5.7 It is further mutually agreed that the question of whether or not this Agreement is to be terminated is one of the issues subject to vote by such a secret, impartially supervised, written ballot.
“5.8 It is further mutually agreed that during the life of this Agreement the Company will not engage in any form of lockout, and the Union will not cause or permit the members of the bargaining unit to take part in any sit-down, stay-in, or slow-down, or any curtailment of work or restriction of production or interference with production, or take part in any strike or stoppage of any kind, or picket the plant, on any matter subject to arbitration, and not in any other matter, until all the bargaining procedure outlined in this Agreement, (including the Grievance Procedure, where applicable, and in all cases the three steps outlined in this Article), have been completely fulfilled.” 113 N. L. R. B. 1288, 1310-1311.
Labor Board v. Darlington Veneer Co., 236 F. 2d 85 (C. A. 4th Cir.); Labor Board v. Corsicana Cotton Mills, 178 F. 2d 344 (C. A. 5th Cir.). Cf. Allis-Chalmers Mfg. Co. v. Labor Board, 213 F. 2d 374 (C. A. 7th Cir.).
See note 1, supra.
See §§ 201 (c) and 203 (c) of the act, 61 Stat. 152, 154, 29 U.S.C. §§ 171 (c) and 173 (c).