The Workers United union said on Monday that thousands of employees at hundreds of Starbucks stores will walk out on the coffee chain's key Red Cup day promotional event this week, citing staffing and scheduling issues.

Starbucks hands out free reusable holiday-themed cups with coffee purchases on the popular promotional event Red Cup day, which falls on Thursday this week, in the midst of the key holiday season.

The Workers United in a statement said that Red Cup day is "one of the most infamously hard, understaffed days for the baristas" at Starbucks, and called on baristas and supervisors at all Starbucks stores to walk out on Nov. 16.

The union had called for protests at more than 100 Starbucks stores at Red Cup day last year.

"We are aware that Workers United has publicized a day of action at a small subset of our U.S. stores next week... Workers United hasn't agreed to meet to progress contract bargaining in more than four months and has yet to deliver on the campaign promises they've made," Starbucks told Reuters in a statement.

Workers United represents more than 360 unionized stores and more than 9,000 Starbucks employees, according to the union's website.

(Reporting by Juveria Tabassum; Editing by Rashmi Aich)