In the Lawlor v. Loewe case of 1914, the United States Supreme Court ruled that secondary boycotts were illegal under the Sherman Antitrust Act. The defendants, members of a hatters' union, had boycotted and encouraged others to boycott non-union-made hats produced by D.E. Loewe & Co., causing significant financial loss for the company. The court held that such actions constituted an unlawful restraint on trade as they interfered with interstate commerce and violated antitrust laws designed to promote competition in business markets. This decision marked one of the first times labor unions were subject to federal antitrust laws and significantly limited their power in disputes with employers.

In the dissenting opinion for Lawlor v. Loewe, Justice Holmes argued that the Sherman Act should not be applied to labor unions as they are not combinations in restraint of trade or commerce among several states. He believed that a strike by workers did not constitute an illegal combination under antitrust laws and was instead a lawful exertion of their rights. Furthermore, he contended that applying such laws to labor disputes would infringe upon workers' constitutional rights to free association and collective bargaining. In his view, the majority's interpretation of the Sherman Act was overly broad and could potentially criminalize any concerted action by employees seeking better working conditions or wages.