The move adds more than 500 to the unionized video game staff at Microsoft, which has pledged to remain neutral on organizing efforts.

More than 500 workers in the team behind World of Warcraft, one of the most popular video games in the world, have voted to unionize, the Communication Workers of America said on Wednesday.

The move expands the ranks of organized labor at Microsoft, which acquired the video game giant Activision Blizzard — whose subsidiary Blizzard Entertainment produces World of Warcraft — for $69 billion last year. To satisfy the regulators overseeing the mega-acquisition, Microsoft promised to remain neutral on unionizing efforts, an unusually permissive policy in the tech industry.

An arbitrator determined on Wednesday that a majority of the World of Warcraft workers, including designers, engineers, artists and quality testers, supported the C.W.A., the union said in a statement.

Blizzard Entertainment recognized the union, increasing the number of unionized game workers at Microsoft to more than 1,750, the C.W.A. said.

World of Warcraft, released in 2004, was a landmark game in the multiplayer role-playing genre. It allowed thousands of players to simultaneously explore a vast fantasy world, and generated billions of dollars in revenue for Blizzard.

Workers staged a walkout at Blizzard Entertainment’s headquarters in 2021 after California’s Department of Fair Employment and Housing accused Activision Blizzard of fostering a culture of sexual harassment and discrimination against female employees.

About 600 workers at Activision Publishing, another Activision Blizzard subsidiary, voted to unionize in March, forming the largest video game workers’ union in the United States. Bethesda Game Studios also joined the C.W.A. last week, adding about 240 more game developers to the group of unionized workers at Microsoft.

Microsoft recognized both unions.