Mastro Plastics Corporation and French-American Reeds Manufacturing Co. (collectively, Mastro) (defendants) employed workers who were represented by Local 3127 of the carpenters’ and joiners’ union (Carpenters). The collective-bargaining agreement (CBA) between Carpenters and Mastro provided that Carpenters would “refrain from engaging in any strike or work stoppage” during the CBA’s one-year term, which expired on November 30, 1950. In August 1950, Local 65 of the Wholesale and Warehouse Workers Union began campaigning to represent Mastro’s employees. Mastro opposed Local 65’s campaign but thought that Carpenters was too weak to handle Local 65’s challenge. Mastro thus asked Carpenters to transfer its bargaining rights to a different union, Local 318. Carpenters refused, and Mastro began inducing employees to join Local 318. In October 1950, Carpenters requested to modify the CBA in anticipation of the current agreement’s expiration, and the parties entered the statutory renegotiating period provided by § 8(d)(4) of the National Labor Relations Act. That section provided that a party giving notice of its desire to terminate or modify a CBA must continue under the current CBA’s terms without resorting to a strike or lockout for a 60-day period. In November 1950, Mastro discharged employee Frank Ciccone for supporting Carpenters and opposing Local 318. In protest, Carpenters engaged in a strike that shut down Mastro’s plant for weeks. Mastro ultimately refused to reinstate Ciccone or the other striking workers. The general counsel of the National Labor Relations Board (NLRB) (plaintiff) alleged that Mastro’s support of Local 318 and discharge of Ciccone and other employees were unfair labor practices. Mastro denied the allegations, asserting that the CBA’s waiver of the right to strike applied to all strikes, including strikes intended solely to protest Mastro’s unfair labor practices (e.g., the interference with the union and firing of Ciccone). Mastro also asserted that because the strike began during the § 8(d)(4) renegotiating period, the strikers had lost their status as employees. The NLRB rejected Mastro’s arguments and ordered Mastro to offer reinstatement and backpay to Ciccone and the other discharged employees. A federal appellate court affirmed, and the United States Supreme Court granted certiorari. The Court first noted that Mastro had blatantly interfered with the employees’ right to choose their own bargaining representative. The Court then analyzed Mastro’s asserted defenses.