George Washington University Hospital is facing a labor complaint after deciding to stop recognizing a union representing roughly 150 of its workers.

The hospital in Washington, D.C.'s Foggy Bottom neighborhood “withdrew recognition” from the union, which represents a group of dietary and housekeeping workers, late in October, said Steven Bernstein, a Fisher Phillips attorney representing the hospital. GWU Hospital granted those workers a raise shortly afterward.

The two parties have been locked in a contentious negotiation over a new...