Yes, that is what the D.C. Court of Appeals ruled in Kiewit Power Constructors Co. v. NLRB. The U.S. Court of Appeals for the District of Columbia Circuit denied an appeal and enforced a NLRB order in favor of two former Kiewit electricians who were fired for allegedly threatening a supervisor who was giving oral warnings to groups of workers because they were taking longer breaks than permitted. One electrician told the supervisor that he had been out of work for a year before the Kiewit project and that if he got "laid off it's going to get ugly and [the supervisor] better bring [his] boxing gloves." Another electrician told the supervisor that he had been out of work for eight months and repeated that "it's going to get ugly." Pursuant to its zero-tolerance workplace violence policy, Kiewit fired the two electricians.
The two workers filed unfair labor practice charges, a complaint was issued, and the ALJ upheld the discharges. In a 2-1 decision, the Board reversed the ALJ's decision and Kiewit appealed. The appeals court agreed with the company that an employee who was engaged in protected concerted activity could "by opprobrious conduct, lose the protection of the Act," but concluded that the Board reasonably found that the statements were not actual physical threats and acknowledged "that the employees were speaking in metaphor." According to Judge Thomas Griffith, "It would defeat [NLRA] Section 7 if workers could be lawfully discharged every time they threatened to 'fight' for better working conditions."
In her dissent, Judge Karen Henderson emphasized that the ALJ had found that the workers' comments "amounted to an outright threat uttered in anger" and the Board should not have overruled the ALJ's credibility determination. Henderson wrote "the board's reinstatement – seconded by my colleagues – of employees who openly challenged, by threatening language, lawful decisions of their employer compels me to observe: 'so much for industrial peace.'"