Associated General Contractors of California, Inc. (General Contractors) (defendant) was a membership corporation composed of various building and construction contractors. The California State Council of Carpenters (the union) (plaintiff) was one of several California unions composed of individuals working in the construction business. Collectively, the California unions represented over 50,000 people. The union and General Contractors negotiated and entered into collective-bargaining agreements covering the union’s workers for over 25 years. The union claimed that General Contractors acted to undermine the union’s collective-bargaining position by coercing third-party contractors not to enter into collective-bargaining agreements with the union and also by coercing contractors and subcontractors to hire nonunion workers. Seeking a remedy, the union brought a lawsuit against General Contractors, claiming that General Contractors’s coercive conduct amounted to an antitrust violation, entitling the union to treble damages under § 4 of the Clayton Act. General Contractors brought a motion to dismiss the union’s claim for treble damages, but the court of appeals allowed the claim to proceed. General Contractors appealed the decision.