In the case of Lewis et al. v. National Labor Relations Board (1957), the U.S Supreme Court ruled in favor of the National Labor Relations Board (NLRB). The dispute arose when a group of employees were fired by their employer for refusing to cross a picket line at another company's premises, which was deemed as disloyal conduct by their employer. The NLRB argued that these dismissals violated Section 8(a)(1) and (3) of the National Labor Relations Act because they interfered with employee rights to engage in concerted activities for mutual aid or protection, regardless if they are unionized or not. On appeal, however, both Circuit Court and Supreme Court held that such activity did not constitute protected concerted activity under this provision since it didn't pertain directly to their own employment conditions but rather involved an external labor dispute between other parties.

In the dissenting opinion for Lewis et al. v. National Labor Relations Board, Justice Frankfurter disagreed with the majority's interpretation of Section 8(b)(4) of the Taft-Hartley Act and its application to this case. He argued that Congress intended to protect neutral employers from being drawn into labor disputes not their own, but did not intend to prevent a union from pressuring an employer with whom it has a direct dispute by picketing at sites where that employer is doing business, even if other businesses are incidentally affected. In his view, applying Section 8(b)(4) in such cases would unduly restrict unions' ability to fight for better working conditions and wages against powerful corporations which often operate through various subsidiaries or contractors. Therefore, he believed that the NLRB was wrong in finding Teamsters Local Union guilty of unfair labor practices when they picketed at retail stores selling bread produced by a bakery they were striking against.