(Bloomberg) -- The group organizing Starbucks Corp. baristas in New York is now seeking to unionize some of their Arizona co-workers, expanding a campaign that could create the first labor outpost among the company’s thousands of corporate-run U.S. stores.

Workers United said it has signed up a majority of employees at a Starbucks store in Mesa, Arizona, and is filing a petition Thursday asking the National Labor Relations Board to hold an election there.

“This is the best way to contribute meaningfully to our partnership with the company and ensure both that our voices are heard and that, when we are heard, we have equal power to affect change and get things done,” employees at the Mesa site wrote in a Tuesday letter to Starbucks Chief Executive Officer Kevin Johnson.

Starbucks didn’t immediately respond to a request for comment Thursday.

The expanded effort underscores the renewed strength of labor across the U.S. as unions capitalize on a tight labor market to push for better pay and working conditions. Organizing efforts have launched this year at a number of major companies, and private-sector union members are authorizing strikes at a rate rarely seen in modern America.

See also: Starbucks union vote sets up watershed moment for labor

The group pushing for the Mesa election had already petitioned for separate votes at six stores in the Buffalo, New York, region, including three that are currently voting in a four-week mail-in election. The other trio’s more-recent filings are still pending with the agency.

Workers United, an affiliate of the Service Employees International Union, has said that its Starbucks campaign in Buffalo arose out of a regional effort to organize restaurants -- such as the locally based Spot Coffee where workers voted to unionize in 2019 -- rather than a national strategy targeting Starbucks. But the Arizona filing shows the campaign’s potential to spread, especially if the union prevails in at least one of the elections now underway.

It took just a few days to sign up the majority of the Mesa store’s staff, according to pro-union employee Michelle Hejduk, who’s been with the company for four years. Workers there have been discussing the Buffalo union campaign since it went public in August, she said. 

“Seeing them doing this was kind of an awakening, like wait, we do have the power and we are stronger together,” she said.

Whistleblower Claims

According to the union, a member of Starbucks management who oversaw the same Mesa store came forward recently as a whistleblower to provide information to employees, the labor board and the New York Times about the company’s anti-union tactics. The union accused Starbucks in a Nov. 4 labor board complaint of responding to organizing “by engaging in a campaign of threats, intimidation, surveillance” and other illegal activity. 

Employees have said the company pressured them to attend meetings in which its representatives warned a union could lead to the loss of some benefits, and deployed out-of-town managers to visit their stores and try to dissuade them from organizing.

Starbucks has said it complies strictly with labor laws. The coffee chain also says it’s not uncommon for higher-ups to visit local stores, and that while it expects employees to attend its meetings, it doesn’t punish them if they refuse.

The company has argued that any union election in the Buffalo region should involve at least all 20 of its restaurants there. It has asked the labor board’s members in Washington, D.C., to overturn the acting regional director’s ruling instead allowing store-by-store votes. If that ruling is upheld, Starbucks would be required to collectively bargain over conditions at any location where a majority of eligible employees vote for the union. 

Ballots from the first three Buffalo stores are due to be received by the NLRB by Dec. 8, but could go uncounted for weeks after that, depending how long the NLRB members take to consider the company’s appeal.

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