Joe Biden, Bernie Sanders, Elizabeth Warren and Andrew Yang on Friday threatened to skip the PBS NewsHour/POLITICO Debate at Loyola Marymount University in Los Angeles next week, asserting they would not cross the picket lines of campus workers locked in a labor dispute.

UNITE HERE Local 11, a union representing 150 cashiers, cooks, dishwashers and servers at the university, said in a statement that it had not yet reached a resolution in negotiations for a collective bargaining agreement with Sodexo — a global services company that employs the workers and is subcontracted by the university to handle food service operations.