About 600 workers at Activision Publishing, the video game maker owned by Microsoft, are unionizing, forming the largest video game workers’ union in the United States, the Communications Workers of America said on Friday. Microsoft recognized the union after the vote count was finalized.

The employees work in quality assurance, testing Activision’s games for bugs, glitches and other defects, and 390 of them voted to form a union, while eight opposed the effort, the union said. About 200 workers did not vote.

Microsoft acquired Activision Blizzard, the maker of Call of Duty and other blockbusters, for $69 billion in October. As part of its lengthy effort to convince regulators to approve the deal, Microsoft signed a first-of-its-kind pact in the industry to remain neutral if workers wanted to unionize with the C.W.A.

Managers were trained not to express an opinion about whether unionization was good or bad, and the C.W.A. said Activision’s management upheld the pact and did not interfere in the workers’ organizing efforts.

“That has been, organizing-wise, a huge blessing,” said Kara Fannon, a member of the union organizing committee who works for Activision near Minneapolis. “It has helped with a lot of people who were concerned about union busting or potential retaliation.”

The new union is the first at Activision since the pact went into effect.

“Microsoft’s choice will strengthen its corporate culture and ability to serve its customers and should serve as a model for the industry,” C.W.A.’s president, Claude Cummings Jr., said in a statement.

The largest group of employees is in Minnesota, though the union also includes offices in Texas and California. The union’s hopes include negotiating higher pay, improving job security and providing more advancement opportunities for the quality assurance testers, who perform some of the lowest-paid work in game development.

The pact also meant workers were able to sidestep the lengthy and often contentious process of petitioning the National Labor Relations Board for an election. Instead, they used an expedited process, where workers indicated their support or opposition for the union by either signing a union authorization card or voting confidentially online in a portal that opened Feb. 22 and closed on Thursday afternoon. A third-party arbiter, Fred Horowitz, verified the results.

After the vote count, Amy Pannoni, a deputy general counsel at Microsoft, said in a statement that the company looked forward to “continuing our positive labor management relationship,” and that it recognized C.W.A. “as the bargaining representative for the Activision Publishing central quality assurance employees.”

Workers had been organizing at Activision since at least 2021, when employees across the company staged a walkout after a California civil rights agency sued the company for workplace sexual misconduct. (The company settled the case on narrower grounds last year.) Over time, workers’ organizing focused on unionization, with the support of the C.W.A.

The workers also saw the successful effort last year to unionize at ZeniMax Media, a video game company also owned by Microsoft, which had expanded its neutrality pact to cover any of the other video game studios it owned. In January 2023, about 300 workers at ZeniMax, whose Bethesda Game Studios makes hits such as The Elder Scrolls, voted to unionize through the new, expedited process.

After Friday’s results, the C.W.A. now represents more than 1,000 video game workers at Microsoft.

The video game industry has been roiled by a series of layoffs and other cost-cutting measures for more than a year. Ms. Fannon said that getting better layoff protections, such as improved severance, has been a common concern among workers even before Microsoft cut 1,900 jobs in its video game division in January, including many layoffs at Activision.