In the 1940 case of International Association of Machinists; Tool and Die Makers Lodge No. 35, Etc. v. National Labor Relations Board, the U.S Supreme Court ruled in favor of the National Labor Relations Board (NLRB). The court held that a labor union's refusal to work overtime constituted an unfair labor practice under Section 8(b)(4) of the National Labor Relations Act (NLRA), which prohibits unions from engaging in secondary boycotts or other coercive activities aimed at neutral employers who are not directly involved in a labor dispute. The decision was significant as it clarified what constitutes an "unfair labor practice" by a union under federal law and affirmed NLRB's authority to regulate such practices.

In the dissenting opinion of this case, it was argued that the National Labor Relations Board (NLRB) had overstepped its authority by intervening in a dispute between a union and an employer regarding wage rates. The dissenting justices believed that such matters should be left to collective bargaining rather than government intervention. They also expressed concern about the potential for abuse of power by the NLRB, arguing that its decision in this case could set a dangerous precedent for future labor disputes. Furthermore, they disagreed with the majority's interpretation of Section 8(5) of the National Labor Relations Act, which prohibits employers from refusing to bargain collectively with their employees' representatives. In their view, this provision did not give the NLRB carte blanche to dictate terms and conditions of employment but merely required employers to engage in good faith negotiations with unions.