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

Starbucks Workers United, the union that has organized workers at 535 company-owned U.S. stores, said Starbucks has failed to honor a commitment made in February to reach a labor agreement.

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.