The strike, which began Friday in Los Angeles, Chicago and Starbucks' hometown of Seattle, spread Monday to stores in Boston, Dallas and Portland, Ore. Workers in New York, Denver, Pittsburgh and other cities had also joined the strike over the weekend.

Unionized Starbucks workers in Boston on Monday joined a nationwide strike to protest lack of progress in contract negotiations with the company.

A rolling strike of Starbucks baristas began Friday and grows to include about 300 of the coffee giant's shops across the U.S.