Workers at more than 100 U.S. company-owned Starbucks locations plan to strike for one day on Thursday to protest what they say is illegal retaliation against their union organizing.

The walkout comes on the one day each year that Starbucks gives away reusable, red, holiday-themed cups to customers with coffee purchases. In the past, the promotion has driven up traffic, resulting in long lines and stores' quickly running out of the cups.

The workers say they are underpaid and don't have consistent schedules. They are also protesting firings, store closures and other actions that they say are illegal retaliation by Starbucks against them for unionizing.

"We're organizing for a voice on the job and a true seat at the table," said Michelle Eisen, an employee in Buffalo, New York.

Starbucks has nearly 9,000 corporate-owned U.S. locations.

Starbucks has said it respects employees' right to organize, that store closings were due to safety concerns and that fired employees violated company policies. The company and union have accused each other of stalling bargaining.

The National Labor Relations Board in August ordered Starbucks to rehire some fired baristas who were union activists.

In just over the past year, about 260 U.S. locations have voted to join the union. Dozens of them began bargaining last month.

After they walk off the job on Thursday, the unionized employees plan to hand out their own version of the red cups - but with their Starbucks Workers United design. 100 (Reporting by Hilary Russ; Editing by Leslie Adler)