Earlier, Starbucks said the union “prematurely ended” a bargaining session and called for talks to continue. The coffee chain has said it’s focused on improving workers’ experience and that baristas who work at least 20 hours a week receive $30 an hour, on average, when combining pay and benefits.

Workers in about 10 to 15 stores across the Los Angeles, Seattle and Chicago areas kicked off the strike, which spread to a similar number of stores in three additional metropolitan areas each day. By Monday, baristas in more than 50 stores in cities like Boston, Dallas, Denver, New York and Philadelphia did not report for work.

Starbucks' union says workers are walking off the job at some 300 — out of over 10,000 — stores across the U.S. as contract negotiations falter.