The AFL-CIO, the nation’s largest labor federation, will itself be the subject of a labor protest Tuesday, when as many as 1,000 members of the Office and Professional Employees International Union are set to gather at the federation’s Washington, D.C., headquarters.

OPIEU Local 2 represents an estimated 50 janitorial workers, secretaries, and other office employees at the AFL-CIO. They voted earlier this week to authorize a strike, claiming that the federation’s leadership was trying to strong-arm them into accepting a contract that their members had already rejected.