In the case of International Longshoremen's Association, Local 1291 v. Philadelphia Marine Trade Association in 1967, the Supreme Court ruled on a dispute between a labor union and an employer association over whether certain work was covered by their collective bargaining agreement. The employer had contracted out some work to non-union workers that the union believed should have been performed by its members under their contract. The National Labor Relations Board (NLRB) initially sided with the employers, but this decision was reversed by an appellate court which held that such subcontracting violated federal law protecting collective bargaining agreements from unilateral changes made without negotiation or consent from both parties involved. The Supreme Court upheld this reversal and agreed with the appellate court’s interpretation of federal labor laws as prohibiting unilaterally decided subcontracting when it affects conditions of employment protected under existing contracts. This ruling affirmed unions' rights to bargain collectively about decisions affecting job security and working conditions for their members.

In the dissenting opinion for International Longshoremen's Association, Local 1291 v. Philadelphia Marine Trade Association, Justice Fortas argued that the majority had misinterpreted Section 8(b)(4) of the National Labor Relations Act (NLRA). He contended that this section was designed to prevent unions from engaging in secondary boycotts against neutral employers, not to prohibit them from striking in support of their own wage demands. According to Justice Fortas, a strike becomes unlawful under Section 8(b)(4) only when it is aimed at forcing an employer or other person "to cease doing business with any other person." In this case, he believed that there was no evidence showing such intent on part of the union; rather they were merely seeking better wages and working conditions for themselves. Therefore, he disagreed with the majority’s decision which held otherwise and found union guilty of violating NLRA.