The work stoppage is expected to be larger than last year’s strike on the same day, but amounts to around 2 percent of Starbucks’s 9,000 cafes nationwide.

Lexi Rizzo fought to unionize her Starbucks.

Leaders of Starbucks Workers United, the union that has organized more than 360 Starbucks locations over the past two years, say the company is illegally stalling and thwarting the bargaining process for workers’ first contract. They are specifically demanding that the company make adjustments to ease stress on workers during big promotional sales event days when stores devolve into chaos with giant backlogs of orders.

“I think Starbucks thinks this movement isn’t going to get bigger, that we’re not strong,” said Jasmine Leli, a striking barista in Buffalo. “But we are in this fight and we’re not going anywhere. We just want safer working conditions, better working conditions for everyone.”

“We have nearly 10,000 stores open right now delighting our customers with the joy of Red Cup Day,” Andrew Tull, a Starbucks spokesman, said in a statement. “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.”

Tull’s statement added that the company remains “ready to progress in-person negotiations” and that it hopes that the union’s “priorities will shift to include the shared success of our partners.”

Workers are also demanding Starbucks turn off mobile ordering on future promotion days, which they say creates a pileup of orders when stores are understaffed and baristas are expected to handle walk-in, drive-through and delivery orders. “Someone and 20 of their friends can put in a mobile order and then a barista is doing the work of two to three people,” Leli said. “It’s a mess at the end of the day.”

The strike arrives as union workers in other industries, such as auto manufacturing, entertainment and health care, have been walking off the job by the thousands — and winning strong union contracts with record wage increases. Most recently, autoworkers at the Big Three Detroit automakers won 25 percent raises over the next 4½ years.

Leli said she and her co-workers have been waiting months to receive a response from Starbucks to their most recent proposals in bargaining.