November 16, Reuters Workers United said on social media platform X that hundreds of Starbucks (SBUX.O) employees had walked out of work during a significant promotional event on Thursday in protest of inadequate staffing and scheduling.

The protest coincides with Starbucks’ Red Cup Day promotion, in which patrons who purchase coffee are given free, reusable, red cups with holiday designs.

More than half of Starbucks’ US locations were open and “serving customers” this morning, the company claimed on Thursday. However, it added that “a few dozen stores with some partners (were) on strike.”

A dozen or so employees demonstrated outside the Starbucks location on the Astor Place campus of New York University, yelling rhymes such as “no contract, no coffee” during their picketing. As this was going on, orders were being placed by NYU employees and students, filling the Astor Place.

Red Cup day has historically provided a big boost to store attendance; Placer.ai data indicates that last year’s visitation to U.S. Starbucks locations increased by 94% compared to the daily average for the whole year.

According to Workers United, which represents over 9,000 Starbucks employees across about 360 U.S. locations, the occasion was one of the “most infamously hard, understaffed days” because drink orders were piling up and staff members were being verbally abused by irate patrons due to lengthy wait times.