An airport services company could legally fire a skycap after he complained about not receiving a tip, the National Labor Relations Board said in a decision narrowing what types of employee activities get the protection of federal labor law.

The skycap’s tip-related comment wasn’t a group action undertaken for mutual aid just because he used the word “we” and spoke to his supervisor in the presence of co-workers, the NLRB’s three Republican members said Jan. 11. The board dismissed an unfair labor practice charge against Alstate Maintenance, a contractor that provides ground services at Kennedy International Airport in New York....