New York City Mayor-elect Zohran Mamdani (D) encouraged his social media followers to boycott Starbucks during a worker strike.

"Starbucks workers across the country are on an Unfair Labor Practices strike, fighting for a fair contract," Mamdani posted on X on Thursday. "While workers are on strike, I won’t be buying any Starbucks, and I’m asking you to join us. Together, we can send a powerful message: No contract, no coffee."

Starbucks Workers United, a union for Starbucks workers, announced Thursday that it was starting an open-ended strike in what is being called the "Red Cup Rebellion," Fox News reported.

Thursday was Starbucks’ Red Cup Day, when customers can pick up a free, reusable festive red cup for the holidays, and is typically one of the company’s busiest days.

"As of today, Starbucks workers across the country are officially ON STRIKE. And we're prepared for this to become the biggest and longest ULP strike in Starbucks history. Say #NoContractNoCoffee with us: DON'T BUY STARBUCKS for the duration of our open-ended ULP strike!" Starbucks Workers United posted on X on Thursday.