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.

It’s four days until Christmas, and all through the U.S. Starbucks employees are picketing for fair labor practices. This strike is expected to be the biggest one yet for the union.