Workers at some Starbucks stores started a five-day strike Friday in three U.S. cities, including Chicago, to protest lack of progress in contract negotiations with the company. S

The workers’ union warns the walkouts could spread to hundreds of cafes by Christmas Eve if Starbucks does not meet demands at the bargaining table.

A five-day strike by Starbucks baristas had closed 59 stores as of Monday afternoon, according to the union organizing the workers.