When a company promises “zero tolerance” for certain workplace wrongdoing, it had better mean it—particularly when unions are involved. One company, Nichols Aluminum, learned this the hard way recently when the National Labor Relations Board found its firing of an employee over violating a zero tolerance policy for violence and threats to be an unfair labor practice.

The problems Nichols Aluminum has faced at the NLRB started with a hand gesture. The company, which has a combination of union and nonunion employees in its Davenport, Iowa, facility, experienced a union-initiated labor strike from January 20, 2012 to April 6, 2012. After the strike ended, returning union employees were asked to sign a form indicating that they would not strike again over the same dispute that had led to the previous strike. A few weeks later, Bruce Bandy, a worker at Nichols who had participated in the strike through Teamsters Local Union No.371, was let go from his job after he made a “cutthroat” gesture (bringing his hand across his neck) at another employee who honked a forklift horn at him. Nichols Aluminum ascertained that Bandy’s gestures had constituted a threat in violation of the company’s zero tolerance policy.