The U.S. Supreme Court case Duplex Printing Press Company v. Deering et al., 1920, revolved around the issue of labor unions and their activities in relation to antitrust laws. The plaintiff, Duplex Printing Press Company, alleged that the defendants (Deering and others as business agents of District No. 15 of the International Association of Machinists) were engaging in a boycott against them which was causing harm to interstate commerce and violating the Sherman Antitrust Act - an act designed to limit monopolies and promote competition for benefit consumers' interests. However, the court ruled in favor of Deering et al., stating that labor unions were exempt from such antitrust legislation under what is known as "labor exemption". This principle holds that union activity is inherently self-regulated by workers’ right to organize; thus it falls outside federal antitrust laws unless it involves non-labor groups or has a secondary boycott characteristic (which aims at neutral third parties). In this case, since no evidence suggested involvement with non-labor entities or secondary boycotting tactics by IAM's district branch members against Duplex company's products sale across state lines – they weren't held liable for any violation.

In the dissenting opinion for Duplex Printing Press Company v. Deering et al., Justice Louis Brandeis argued that labor unions should be allowed to engage in peaceful picketing and boycotts as a means of exerting economic pressure on employers, even if these actions might disrupt interstate commerce. He contended that Congress did not intend the Sherman Antitrust Act to apply to labor disputes when it passed the law in 1890, and he criticized his colleagues for interpreting it too broadly. According to Brandeis, this expansive interpretation threatened workers' rights by potentially criminalizing their efforts to improve working conditions or wages through collective action. Furthermore, he believed that courts should refrain from intervening in such disputes unless absolutely necessary because they were ill-equipped to handle complex social and economic issues best left up policymakers.