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. The company urges it to return to the bargaining table.

A strike at Starbucks will expand to over 300 U.S. stores on Tuesday, with more than 5,000 workers expected to walk off the job before the five-day work stoppage ends later on Christmas Eve, the workers' union said.