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.

The strike, which began Friday in Los Angeles, Chicago and Starbucks’ hometown of Seattle, continued spreading to stores across the country over the weekend.