A union representing more than 10,000 Starbucks employees said Tuesday that a strike that began Friday had expanded to include more than 300 stores as part of a planned five-day walkout.

Workers in about 10 to 15 stores across the Los Angeles, Seattle and Chicago areas kicked off the strike, which spread to a similar number of stores in three additional metropolitan areas each day. By Monday, baristas in more than 50 stores in cities including Boston, Dallas, Denver, New York and Philadelphia did not report for work.

The strike spread to additional cities Tuesday, union representatives said, including at least one in the Bay Area, where some baristas were already on strike, potentially dampening business at one of the company’s busiest times of the year. Closed stores are expected to reopen Wednesday, when workers have said they would return to work.

A typical company-owned Starbucks store in the United States brings in sales of about $4,000 to $8,000 during a normal business day, according to a former company official and a review of company financial filings. The figures tend to be higher in December.

A Starbucks spokesperson said Monday he could not confirm the sales figure.

The union, Workers United, represents Starbucks employees at more than 500 company-owned stores across the country, about 5% of the U.S. total. It said it called the strike because Starbucks had yet to resolve more than 150 unfair-labor-practice charges on issues like retaliatory firings and cuts to hours, and because Starbucks had not offered a substantial wage increase during contract negotiations.

In the most recent bargaining session, which took place last week, the company offered to guarantee baristas a wage increase of at least 1.5% a year. If the company raised wages for all retail employees more than that — as it did with a recently announced 2% increase for the least experienced workers — unionized baristas would get the higher amount.

“After all Starbucks has said about how they value partners throughout the system, we refuse to accept zero immediate investment in baristas’ wages,” Lynne Fox, the president of Workers United, said in a statement. “Union baristas know their value, and they’re not going to accept a proposal that doesn’t treat them as true partners.”

Starbucks said in a statement Monday that “the overwhelming majority of Starbucks stores across the country have opened as planned” during the past few days, adding that the company is “ready to continue negotiations when the union comes back to the bargaining table.”

It is unclear how many of the striking stores have been shut down. The company said Tuesday morning that about 170 stores “did not open as planned,” while the union said at least 290 locations had closed by noon.

The union campaign at Starbucks began in the Buffalo, New York, area in 2021 and spread across the country the next year. Starbucks had largely resisted union organizing by its baristas until February of this year, when it negotiated a peace deal of sorts with the union.

The two sides agreed to a process that would allow baristas to unionize without opposition from the company, and to monthly bargaining sessions to negotiate a national contract framework. The sessions began in April, and both sides said they hoped to complete the framework by the end of the year.

The two sides also agreed to work to resolve lawsuits and formal accusations of labor law violations that had accumulated during the union campaign. They have resolved hundreds of such cases so far.