Workers hit the picket lines at four Starbucks locations in Philadelphia.
"We demand full staffing. We are consistently understaffed. And it's not just this store, it's the number one problem across all stores," said barista Sal Hirsch.
" We should not have to be sprinting the entire time we are here to get your drinks," added barista Tom Vu.
Workers also say they want better safety and more money.
"Just recently they brought up the starting pay to $15 an hour, but that was after our union drive started," said Sarah Shields.
The walkouts coincide with Starbucks' annual Red Cup Day, when the company gives free reusable cups to customers who order a holiday drink. Workers say it's often one of the busiest days of the year. Starbucks declined to say how many red cups it plans to distribute.
Workers say they're seeking better pay, more consistent schedules and higher staffing levels in busy stores. Starbucks opposes the unionization effort, saying the company functions best when it works directly with employees. The Seattle coffee giant has more than 9,000 company-owned stores in the U.S.
Stores in 25 states planned to take part in the labor action, according to Starbucks Workers United, the group organizing the effort. Some workers planned to picket all day while others planned shorter walkouts. The union said the goal was to shut the stores down during the walkouts.
Workers say attempts to negotiate with the coffee giant have been unsuccessful.
"The workers have been clawing away trying to make improvements to the working condition. But because the company has been refusing to bargain in good faith and purposely understaffing union stores, workers across the country decided today was a good day to coordinate a national day of action," said Alex Riccio, an organizer for Workers United.
Starbucks released a statement to Action News saying, "In those stores where partners have elected union representation, we have been willing and continue to urge the union to meet us at the bargaining table to move the process forward in good faith. "
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At least 257 Starbucks stores have voted to unionize since late last year, according to the National Labor Relations Board. Fifty-seven stores have held votes where workers opted not to unionize.
Starbucks and the union have begun contract talks at 53 stores, with 13 additional sessions scheduled, Starbucks Workers United said. No agreements have been reached so far.
The process has been contentious. Earlier this week, a regional director with the NLRB filed a request for an injunction against Starbucks in federal court, saying the company violated labor law when it fired a union organizer in Ann Arbor, Michigan. The regional director asked the court to direct Starbucks to reinstate the employee and stop interfering in the unionization campaign nationwide.
It was the fourth time the NLRB has asked a federal court to intervene. In August, a federal judge ruled that Starbucks had to reinstate seven union organizers who were fired in Memphis, Tennessee. A similar case in Buffalo has yet to be decided, while a federal judge ruled against the NLRB in a case in Phoenix.
Meanwhile, Starbucks has asked the NLRB to temporarily suspend all union elections at its U.S. stores, citing allegations from a board employee that regional officials improperly coordinated with union organizers. A decision in that case is pending.
Starbucks workers have this message for customers: "I want customers to know that we do care. I know so many of them, their names, their drink orders, and I am happy to see them every day when they walk into the store ... It's just Starbucks says that we strive to fill others' cups, but it's hard when I am not getting the support that I need from corporate," said barista Lydia Fernandez.
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The Associated Press contributed to this report.