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

Workers at more than a dozen Chicago area Starbucks were on strike Christmas Eve, union organizers said, as baristas escalated a national walkout that began in three cities, including Chicago, on Friday.

Starbucks workers have expanded their strike to more cities and closed 59 stores across the U.S. as of Monday, the union said amid stalled negotiations.