Progressive politicians, including democratic socialist New York Mayor-elect Zohran Mamdani, have thrown their support behind thousands of striking Starbucks workers, calling for a boycott of the coffee giant until employees' contract demands are met.

"Starbucks workers across the country are on an Unfair Labor Practices strike, fighting for a fair contract," Mamdani wrote Thursday night on X. "While workers are on strike, I won't be buying any Starbucks, and I'm asking you to join us."

Mamdani's backing represents an early indication of how he might use the bully pulpit of his office, Business Insider reported.

The former New York state assemblyman has long styled himself as pro-union.

The strike began Thursday when roughly 1,000 workers across 65 stores walked off the job, according to Starbucks Workers United.

Thursday was Starbucks' Red Cup Day, when customers receive a reusable cup with the purchase of a holiday-themed drink — typically one of the company's highest-traffic days of the year.

The work stoppage could expand to more than 500 stores if negotiations do not resume, the union said in a news release. Starbucks has 16,864 U.S. stores, according to its latest earnings report, and unionized locations represent about 9,500 baristas — roughly 4% of the retail workforce — Business Insider reported, citing a Starbucks spokesperson.

"I stand in solidarity with @SBWorkersUnited and say #NoContractNoCoffee," Rep. Rashida Tlaib, D-Mich., wrote Thursday on X. "When we strike, we win!"

Rep. Yassamin Ansari, D-Ariz., wrote Friday on X: "Starbucks isn't struggling. $3.6BN in profits last year and a $96M CEO payout. Now its workers are on an Unfair Labor Practices strike. … I'm proud to stand w/ them. Arizonans, I hope you'll join me. #NoContractNoCoffee."

Sen. Ed Markey, D-Mass., posted Thursday on X: "I am in solidarity with @SBWorkersUnited as they strike for the wages, working conditions, and respect they deserve. Starbucks must put an end to their union busting and negotiate in good faith."

Newsmax has reached out to Starbucks for comment. In a Nov. 5 statement, the company said it has "for months ... been at the bargaining table, working in good faith with Workers United."

"We remain committed to meeting regularly with Workers United," the company said, adding that fewer than 4% of its "green apron partners" work in unionized stores and that U.S. locations "remain open and serving customers."