A union organized a strike at a Nichols Aluminum, LLC (Nichols) (defendant) plant. Most workers participated, but a few crossed the picket line. Afterward Nichols required returning workers to take a “no-strike pledge” to not “strike again over the same dispute.” Employee Bruce Bandy participated in the strike but did not play a central role and took the pledge verbally when he returned to work. Nichols also held a meeting to review its long-standing “zero-tolerance” policy toward workplace violence, which subjected anyone who engaged in threatening or violent conduct to immediate termination. Two weeks later, when a worker who had crossed the picket line blared a forklift horn at Bandy, Bandy drew his thumb across his neck in a “cutthroat” gesture. The forklift driver took the gesture as a threat and reported Bandy, even though workers at the plant often used the gesture to signal shutting off or stopping something, and a witness perceived Bandy’s gesture to mean “stop blaring the horn.” Bandy claimed he was just scratching his throat, but Nichols fired him for violating its zero-tolerance policy. However, Nichols did not terminate a replacement worker who cursed at another employee and physically blocked him from getting in his car or a second replacement worker who verbally threatened to “beat” someone. The union filed unfair-labor-practice charges with the National Labor Relations Board (plaintiff), arguing that the no-strike pledge was unlawful and that Nichols treated workers who participated in the strike differently than replacement workers. The administrative law judge (ALJ) found that Nichols did not violate the National Labor Relations Act by terminating Bandy for the cutthroat gesture. The board adopted many of the ALJ’s findings but reversed, concluding that hostility toward the union motivated Bandy’s termination.