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

The Starbucks baristas strike is spreading to more cities — and the union organizing the workers warned the walkout would affect hundreds of stores on Christmas Eve, the last day of the five-day walkout.

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.