Thousands of Starbucks Corp. baristas went on strike Thursday, claiming the coffee chain refuses to fairly negotiate with their union.

The work stoppage is pegged to the company’s Red Cup Day, when Starbucks gives out holiday-themed reusable cups. Workers United, an affiliate of the Service Employees International Union, said staff at hundreds of cafes are participating. It’s one of several tactics — along with outreach to politicians and to students on campuses where Starbucks has contracts — that the union has deployed in an effort to make the company change its behavior.

Thursday’s strike took place in more than 200 US cities and is the largest to date, the union said. Employees at several non-union cafes around the country launched surprise strikes Thursday and plan to petition soon to organize, Workers United said. The stoppage is a repeat of last year, when baristas went on strike at 113 cafes on Red Cup Day.

Starbucks said it has nearly 10,000 stores open. “There are also a few dozen stores with some partners on strike, and more than half of those stores are open this morning serving customers,” the company said in an email.

Starbucks shares rose 0.9% at 1:44 p.m. in New York trading. The stock has gained about 8% this year, roughly half the advance of the S&P 500 Index.

At a Starbucks location at New York’s Astor Place, nine out of 10 staffers scheduled to work didn’t show up for their shifts, Starbucks Workers United said. At around 9:20 a.m., a dozen people, including workers, were marching outside with signs that read “No Contract No Coffee.”

The store had about eight workers inside and around 30 customers waiting for drinks. The staffers working inside the location were mostly managers, the union said. A union organizer told several customers walking into the store that they were crossing a picket line by going inside the cafe. Several continued on anyway.

Nearly two years have passed since Workers United notched its first landmark victory at a Starbucks cafe in Buffalo, New York. Since then, more than 350 of the chain’s 9,000 corporate-run US locations in more than 40 states have voted to join the union. But none of the locations has come close to securing a union contract with the company, and the pace of the union’s growth has drastically slowed.

Regional directors of the US National Labor Relations Board have issued more than 100 complaints against the company, alleging illegal anti-union tactics including closing stores, firing activists, and refusing to fairly negotiate at unionized cafes.

Starbucks has denied wrongdoing, and has said the union is the one refusing to negotiate in good faith. The company said this week that it hopes the union’s “priorities will shift to include the shared success of our partners and working to negotiate union contracts for those they represent.”

As part of the strike, workers are demanding Starbucks turn off mobile ordering on promotion days in the future, which they say the company is scheduling with increasing frequency. Workers say that mobile orders, which are a key part of the company’s growth strategy, add complexity to an already overburdened workload amid a staggering array of options.

Starbucks has announced pay increases for baristas and is upgrading its kitchens to streamline beverage preparation.

Edwin Palma Solis, a 24-year-old barista who has worked at the Astor Place location for two years, said Starbucks has repeatedly rescheduled negotiating sessions with the union. He added the store doesn’t have enough workers.

“We don’t typically get much staffing,” he said. “This is something we face everyday.”

One customer, Shanee Samuels, decided not to pick up a mobile order after seeing the striking workers. She said she plans to call the company to get a refund. “I support union workers,” Samuels said.

This article was provided by Bloomberg News.