Starbucks Workers United launched an open-ended strike in more than 40 cities Thursday on Red Cup Day, one of the chain’s biggest sales days of the year.

The protest, which the union says involves more than 1,000 baristas in over 65 stores, comes after Workers United voted to authorize an open-ended strike after baristas and the coffee giant failed to reach a collective bargaining agreement.

The strike could hurt business during Starbucks’ busy holiday season, which typically provides a sales boost and will be key to the chain’s plan to turn around performance in the U.S. under new CEO Brian Niccol. Starbucks broke a nearly two-year streak of same-store sales declines in its most recently reported quarter. Past strikes have impacted less than 1% of its stores, the company said.

The union is pushing for improved hours, higher wages and the resolution of hundreds of unfair labor practice charges levied against Starbucks. The two parties have not been in active negotiations to reach a contract after talks between them fell apart late last year.

Starbucks and the union entered into mediation in February, and hundreds of barista delegates voted down the economic package Starbucks proposed in April. Both sides have pointed blame at the other for failure to reach a bargaining agreement, and say they’re ready to negotiate.

Workers United, which began organizing at Starbucks in 2021, says it now represents more than 12,000 workers across more than 550 stores. The company last week told CNBC that the union only represents 9,500 workers at 550 cafes.

The baristas say they are prepared to escalate the work stoppage, threatening to make this “the largest, longest strike in company history if Starbucks fails to deliver a fair union contract and resolve unfair labor practice charges.” It is seeking new proposals that address its top issues to finalize a contract.

“If Starbucks keeps stonewalling a fair contract and refusing to end union-busting, they’ll see their business grind to a halt,” Starbucks Workers United spokesperson Michelle Eisen, a former barista who spent 15 years at the company, said in a statement. “No contract, no coffee is more than a tagline — it’s a pledge to interrupt Starbucks operations and profits until a fair union contract and an end to unfair labor practices are won. Starbucks knows where we stand.”

In response to the strike vote results last week, Starbucks previously said it will be ready to serve customers across its nearly 18,000 company-operated and licensed stores this holiday season.

“Starbucks offers the best job in retail, including more than $30 an hour on average in pay and benefits for hourly partners. Workers United, which represents only 4% of our partners, chose to walk away from the bargaining table. We’ve asked them to return—many times. If they’re ready to come back, we’re ready to talk. We believe we can move quickly to a reasonable deal,” Starbucks spokesperson Jaci Anderson told CNBC in a statement Monday.

In a letter to workers addressing the strike authorization vote last week, Sara Kelly, chief partner officer at Starbucks, echoed the belief that the sides could reach an agreement swiftly.

“For months, we were at the bargaining table, working in good faith with Workers United and delegates from across the country to reach agreements that make sense for partners and for the long-term success of Starbucks,” Kelly said. “We reached more than 30 tentative agreements on full contract articles.”

“Our commitment to bargaining hasn’t changed,” she added. “Workers United walked away from the table but if they are ready to come back, we’re ready to talk. We believe we can move quickly to a reasonable deal.”