Act, even though League Law 13 purported to render the resignations ineffective. We defer to the Board's interpretation of the Act and so affirm the judgment of the Court of Appeals enforcing the Board's order. JUSTICE WHITE, concurring. It is so ordered. I agree with the Court that the Board's construction of §§ 7 and 8(b)(1)(A) is a permissible one and should be upheld. The employee's rights under §7 include, among others, the right to refrain from joining or assisting a labor organization and from engaging in concerted activities for mutual aid or protection. The right to join or not to join a labor union. includes the right to resign, and § 8(b)(1)(A) forbids unions to interfere with that right except to the extent, if any, that such interference is permitted by the proviso to that section, which preserves the union's right to prescribe its own rules with respect to the acquisition or retention of membership. The proviso might be read as permitting restrictions on resignation during a strike, since they would seem to relate to the "retention" of membership. But it can also be sensibly read to refer only to the union's right to determine who shall be allowed to join and to remain in the union. The latter is the Board's interpretation. Under that view, restrictions on resignations are not saved by the proviso, and the rule at issue in this case may not be enforced. For the Act to be administered with the necessary flexibility and responsiveness to "the actualities of industrial relations," NLRB v. Steelworkers, 357 U. S. 357, 362–364 (1958), the primary responsibility for construing its general provisions must be with the Board, and that is where Congress has placed it. "[W]e should 'recognize without hesitation the primary function and responsibility of the Board"" to apply these provisions to particular, and often complex, situations. Ford Motor Co. v. NLRB, 441 U. S. 488, 496 (1979), quoting NLRB v. Insurance Agents, 361 U. S. 477, 499 (1960). 95 BLACKMUN, J., dissenting Where the statutory language is rationally susceptible to contrary readings, and the search for congressional intent is unenlightening, deference to the Board is not only appropriate, but necessary. This is such a case. The Board has adopted a sensible construction of the imprecise language of §§ 7 and 8 that is not negated by the legislative history of the Act. That Congress eliminated from the bill under consideration a provision that would have made certain restrictions on resignation unfair labor practices falls short of indicating an intention to foreclose the Board's reading. By the same token, however, there is nothing in the legislative history to indicate that the Board's interpretation is the only acceptable construction of the Act, and the relevant sections are also susceptible to the construction urged by the union in this case. Therefore, were the Board arguing for that interpretation of the Act, I would accord its view appropriate deference. Because I do not understand it to be inconsistent with the foregoing views, I join the Court's opinion. JUSTICE BLACKMUN, with whom JUSTICE BRENNAN and JUSTICE MARSHALL join, dissenting. Today the Court supinely defers to a divided-vote determination by the National Labor Relations Board that a union commits an unfair labor practice when it enforces a worker's promise to his fellow workers not to resign from his union and return to work during a strike, even though the worker freely made the decision to join the union and freely made the promise not to resign at such a time, and even though union members democratically made the decision to strike in full awareness of that promise. The Court appears to adopt the NLRB's rule that enforcement of any such promise, no matter how limited and no matter how reasonable, violates the breaching worker's right to refrain from concerted activity. The Board's rule, however, finds no support in either the lan BLACKMUN, J., dissenting 473 U. S. guage of §§ 7 and 8(b)(1)(A) of the National Labor Relations Act on which the Court purports to rely, or in the general goals of the Act, which it ignores. Accordingly, the undeserved deference accorded that rule has produced a holding that improperly restricts a union's federally protected right to make and enforce its own rules, and at the same time traduces the broader aim of federal labor policy implicated by this right: to preserve the balance of power between labor and management by guaranteeing workers an effective right to strike. I Having determined that the individual worker standing alone lacked sufficient bargaining power to achieve a fair agreement with his employer over the terms and conditions of his employment, Congress passed the NLRA in order to protect employees' rights to join together and act collectively. See 29 U. S. C. § 151. Thus, the heart of the Act is the protection of workers' §7 rights to self-organization and to free collective bargaining, which are in turn protected by §8 of the Act. 29 U. S. C. §§ 157 and 158. Because the employees' power protected in the NLRA is the power to act collectively, it has long been settled that the collective has a right to promulgate rules binding on its members, so long as the employee's decision to become a member is a voluntary one and the rules are democratically adopted. When these requirements of free association are met, the union has the right to enforce such rules "through reasonable discipline," including fines. See NLRB v. AllisChalmers Mfg. Co., 388 U. S. 175, 181 (1967). Unless internal rules can be enforced, the union's status as bargaining representative will be eroded, and the rights of the members to act collectively will be jeopardized. Ibid. "Union activity, by its very nature, is group activity, and is grounded on the notion that strength can be garnered from unity, solidar 55 95 BLACKMUN, J., dissenting ity, and mutual commitment. This concept is of particular force during a strike, where the individual members of the union draw strength from the commitments of fellow members, and where the activities carried on by the union rest fundamentally on the mutual reliance that inheres in the 'pact."" NLRB v. Textile Workers, 409 U. S. 213, 221 (1972) (dissenting opinion); see Allis-Chalmers, 388 U. S., at 181. It is in the proviso to §8(b)(1)(A), 29 U. S. C. §158(b) (1)(A), that Congress preserved for the union the right to establish "the contractual relationship between union and member." Textile Workers, 409 U. S., at 217. Recognizing "the law which normally is reflected in our free institutions," id., at 216, Congress in the proviso preserved a union's status as a voluntary association free to define its own membership. The proviso states that the creation of a union unfair labor practice for a violation of the workers' right to refrain from collective action does not "impair the right of a labor organization to prescribe its own rules with respect to the acquisition or retention of membership therein." 29 U. S. C. § 158(b)(1)(A). As the Court has recognized previously and now concedes, the legislative history indicates that the proviso was meant to ensure that the employees' "right to refrain" would not be understood "to interfere with the internal affairs or organization of unions." Ante, at 102, quoting Allis-Chalmers, 388 U. S., at 187, in turn quoting 93 Cong. Rec. 4272 (1947) (statement of Sen. Ball). The "right to refrain" simply "was not intended to give the Board power to regulate internal union affairs, including the imposition of disciplinary fines, with their consequent court enforcement, against members who violate the unions' constitutions and bylaws." NLRB v. Boeing Co., 412 U. S. 67, 71 (1973). See also Scofield v. NLRB, 394 U. S. 423, 428 (1969). Sensitive to both the Act's central goal of facilitating collective action, and the Taft-Hartley Act's protection against coercion of employees, the Court previously has interpreted the proviso to distinguish between two kinds of union rules. BLACKMUN, J., dissenting 473 U. S. Reasonable union rules that represent obligations voluntarily incurred by members were intended to be free from federal regulation under §8, while union rules that seek to coerce an employee by utilizing the employer's power over his employment status, or otherwise compel him to take on duties or join in concerted activities he never consented to, were intended to be subject to regulation by the Board. Because rules that regulate the relationship between the union and his employer could be used to coerce an employee into becoming involved with the union in order to protect his job, such rules would impair the employee's free association rights. "[T]he repeated refrain throughout the debates on §8(b)(1)(A) and other sections [was] that Congress did not propose any limitations with respect to the internal affairs of unions, aside from barring enforcement of a union's internal regulations to affect a member's employment status." Allis-Chalmers, 388 U. S., at 195. The proviso was designed "to make it clear that . . . [a]ll we are trying to cover [in §8] is the coercive and restraining acts of the union in its efforts to organize unorganized employees." 93 Cong. Rec. 4433 (1947) (statement of Sen. Ball). Until today, the Court has rejected the proposition that the proviso does not protect a union rule merely because the rule has an impact beyond the confines of the labor organization, Scofield, 394 U. S., at 431-432, or because it is not a rule about the expulsion of members. Cf. ante, at 108-110. League Law 13 is an internal union rule, a "rule with respect to the acquisition or retention of membership" protected by the proviso to §8(b)(1)(A). It requires that employees who freely choose to join the union promise to remain members during a strike or lockout, as well as during the time when a strike or lockout appears imminent. In other words, the rule imposes a condition upon members of the bargaining unit who would like to acquire membership rights. The rule stands for the proposition that to become a union member one must be willing to incur a certain obligation upon |