The victory was the union’s first outside Buffalo and appeared to underscore its momentum in organizing company employees across the country.First they won in Buffalo. Now they’ve scored a victory on the other side of the country.On Friday, the National Labor Relations Board announced that workers at a Starbucks in Mesa, Ariz., had voted 25 to 3 to unionize, with three challenged votes. The result brought the number of company-owned stores with a union to three, out of roughly 9,000 nationwide.The victory was the first for the union since two stores voted to unionize in Buffalo in December, but it could mark the beginning of a larger trend. More than 100 Starbucks stores across more than 25 states have filed petitions for union elections, most of them since that first victory. The next tally will probably come from three more stores in the Buffalo area, where votes have already been cast. Starbucks workers in cities including Boston, Chicago and Seattle are scheduled to vote or are likely to vote in the coming months.“This is another historic moment for Starbucks partners and service industry workers across the country,” Michelle Hejduk, a shift supervisor at the store, said in a statement. “This movement started in Buffalo, and we’ve now brought it across the country.”Reggie Borges, a Starbucks spokesman, said in a statement that the company’s position had not changed. “As we have said throughout, we will respect the process and will bargain in good faith guided by our principles,” he said, adding: “We hope that the union does the same.”Lawyers who advise companies on labor relations said Workers United, an affiliate of the Service Employees International Union, appeared to have considerable momentum in organizing Starbucks workers.“Clearly the work force is very sympathetic to what the union is selling,” said Brian West Easley, a management-side lawyer with Jones Day. “Right now, they probably rightfully believe they have the upper hand, given the number of petitions filed each week.”The company has generally sought to challenge the union store by store, contesting the voting pool for each election before the labor board and sending company officials to cities where workers have filed for elections, partly to share its concerns about unionizing. The challenges delayed the counting of votes in Mesa and the second round of Buffalo stores.But Mr. Easley argued that it would become more difficult for Starbucks to sustain that approach if the company continued to suffer defeats, especially as the number of stores filing for elections increases.“The bigger this gets, the more stretched resources become and the more ineffective they become,” he said. “The ability to push back is eroding as the numbers increase.”At least one prominent Starbucks investor echoed that concern, arguing that the company appeared to be wasting money in its efforts to resist the union. “The company is devoting quite a bit of time and money to putting forward these arguments in front of the N.L.R.B.,” said Jonas Kron, the chief advocacy officer of Trillium Asset Management, which makes investments to further environmental, social and governance goals and had a roughly $43 million stake in Starbucks at the end of last year. “It doesn’t feel like they’re using investor resources — stakeholder resources — that well.”Mr. Kron and Trillium have urged the company to take a neutral stand toward the union. Other labor experts suggested it may eventually be forced to do so whether it wants to or not.“I’m sure there will be a tipping point at some point,” said Amy Zdravecky, a management-side lawyer at Barnes & Thornburg. “How many losses do you have before you change strategy?”Ms. Zdravecky added that the union’s ability to win an election in a state not normally sympathetic to organized labor suggested that the campaign had staying power, and that one risk for Starbucks’s approach to opposing the union is that it could begin to alienate the company’s liberal-leaning customer base.“Fighting unions may not align with where they want to be elsewhere,” she said.Many of the issues that workers in Mesa cited in their decision to support the union were similar to those identified by workers in Buffalo, like staffing and Covid-19 safety. Liz Alanna, a shift supervisor at the store, said that customers sometimes waited 45 minutes last fall after submitting a mobile order because there were not enough baristas to handle the volume. “The lobby would be full of people waiting,” Ms. Alanna said. .The Mesa campaign had an additional subplot that raised the stakes for workers. In early October, the store’s manager, Brittany Harrison, was found to have leukemia. The company initially appeared to rally behind her, Ms. Harrison said in an interview, but its posture later changed.“I’d reach out to the district manager and it would go to voice mail or ring forever and she wouldn’t call back,” she said. Ms. Harrison, and other workers like Ms. Alanna, said that she repeatedly sought an assistant manager to help at the store but that none was forthcoming.The situation came to a head on Friday, Nov. 12, when Ms. Harrison became ill at the store, then put in her two-week notice. The workers at the store filed their petition for a union election the following week. “We really had an easy time moving forward,” said Ms. Alanna, citing frustration over how the company had treated Ms. Harrison. Mr. Borges said that the company had offered Ms. Harrison support throughout her time there, and that it had offered to provide an assistant manager if she went on leave, which she had yet to do. Starbucks’s approach to the union election in Mesa resembled its approach in Buffalo. The company sent a variety of officials to the store — including two new managers, at least two new assistant managers, a senior human resources official based in Colorado, a senior manager who had worked in California and a regional vice president based in Colorado.Workers said they felt the managers and other officials were partly there to monitor them. Ms. Hejduk said the new managers appeared to implement a policy in which at least one manager must be in the store at all times to “babysit,” as she put it.Ms. Hejduk said she had been told on a recent weekday morning that the store was closing and that her shift was being canceled because no manager was available to come in, even though she has a key and frequently worked in the store without a manager before the union election filing. She said the policy was relaxed after the union voting ended.In Mesa, as in at least one of the Buffalo stores, Starbucks also brought in several new workers after the election filing, who typically had spent a few weeks training at other stores. The union argued that the offsite training was meant to ensure that workers began their employment with no contact with union supporters and that the workers were brought in to dilute support for the union. The union, which argues that some of the new workers had not worked at the store long enough to be eligible to vote, won a challenge on similar grounds in Buffalo.Mr. Borges said the officials were addressing operational issues like staffing and soliciting input from workers and educating them about the risks of unionizing, though he said Starbucks respected the rights of its employees to unionize. He said that having a separate location focused on instructing new employees allowed the company to train them more efficiently, and that all of the workers who received ballots were eligible under N.L.R.B. rules. He said it was occasionally a policy to have one manager on at all times when there was new leadership in a store.The count in Mesa and at the three additional Buffalo-area stores had been held up by management challenges over a key legal issue: the proper voting pool for the union elections.In a rebuff to Starbucks, the labor relations board ruled Wednesday that stores could vote individually, rather than having to cast ballots with other stores in a geographic area. The board’s detailed ruling makes it more difficult for Starbucks to get its way on the issue elsewhere.Unions typically favor voting on a smaller scale to reduce the number of votes needed to secure a majority in at least some locations, but Starbucks has argued that stores in the same market are akin to a single unit because employees can work at multiple locations and because district managers oversee them as a cohesive group.One option for Starbucks in light of its recent defeats, said Mr. Easley of Jones Day, would be to resign itself to a union presence and position the company to minimize the union’s influence. He suggested, for example, that Starbucks might focus its opposition on cities where the union had already won, to make sure there weren’t several unionized stores that would provide it with greater leverage.“The next phase of this may be divide and conquer,” he said. “Make sure they don’t end up with voting blocks that could shut down business in a market.”He added, referring to the union: “If they can control market in a particular location, they have leverage to get Starbucks to do something.” More