The action has drawn support from New York Mayor-elect Zohran Mamdani, who urged his followers to boycott the coffee chain.

In an X post, Mamdani, who recently won the mayoral election, wrote: "Starbucks workers across the country are on an Unfair Labor Practices strike, fighting for a fair contract."

He said: "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."

The union, Starbucks Workers United, confirmed that the strike is open-ended and warned it could become the largest and longest unfair labor practices (ULP) strike in Starbucks’ history.

The union called on supporters to join the campaign using the hashtag #NoContractNoCoffee.

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The labour dispute stems from unresolved economic issues and hundreds of ULP charges filed by the union.

Talks for a contract agreement collapsed in the spring, leaving both sides at an impasse, according to the BBC.

US politician Bernie Sanders also expressed support for the striking workers on X: "I stand in solidarity with the Starbucks workers on strike. When a corporation can pay $96 million to its CEO for just four months of work, it can afford to pay its workers a living wage and decent benefits."