In the case of National Woodwork Manufacturers Association et al. v. National Labor Relations Board, 1966, the U.S Supreme Court ruled in favor of a union that had been accused by an employer's association of unfair labor practices. The dispute arose when carpenters' unions insisted on using hand tools instead of pre-cut doors during construction projects as part of their collective bargaining agreements to protect jobs from being lost to mechanization and prefabrication processes. The employers argued this was a violation under federal law which prohibits secondary boycotts - actions intended to influence parties not directly involved in a labor dispute. However, the court held that such work preservation clauses were lawful primary activity protected by federal law since they aimed at preserving work traditionally performed by employees rather than seeking to embroil neutral employers or affect entities with whom the Union has no immediate employer-employee relationship.

In the dissenting opinion for National Woodwork Manufacturers Association et al. v. National Labor Relations Board, Justice Harlan argued that the majority had overstepped its bounds by interpreting labor law in a way that was not intended by Congress. He contended that the union's demand to prohibit subcontracting of work was an illegal secondary boycott under Section 8(b)(4) of the NLRA because it aimed at affecting business relations between neutral employers and their chosen contractors rather than improving workers' conditions directly with their own employer. Furthermore, he believed this interpretation would lead to unnecessary federal intervention in local labor disputes and could potentially disrupt balance within industries as unions might use such demands to exert pressure on unrelated third parties or even entire markets beyond their direct employment relationship.