LOS ANGELES (Reuters) -Union video game actors filed an unfair labor practice charge and declared a strike on Tuesday against the company Formosa Interactive, which provides voiceover services for the popular online game "League of Legends," the actors' union said.

SAG-AFTRA union members have stopped providing covered performance services to "League of Legends," and the massive multiplayer online battle arena game, developed by Riot Games in 2009, is now listed by the union as a struck game.

"The complaint comes after Formosa tried to 'cancel' one of its struck video games shortly after the start of SAG-AFTRA's video game strike," the union said in a statement.

"When they were told that was not possible, they secretly transferred the game to a shell company and sent out casting notices for 'NON-UNION' talent only."

The union said the transfer violated performers' rights to strike under labor laws.

Formosa said it rejects SAG-AFTRA's allegations and has not undermined union rights in any way.

"We believe the strike of 'League of Legends', a game unrelated to the union's claims, is not appropriate," it said in a statement.

Formosa "stands with developers, publishers, platform holders, and talent" and promotes ethical game development, it added.

Riot Games said in a statement on Tuesday that "League of Legends" had nothing to do with the union's claims and had "never once suggested" Formosa should engage with non-union performers.

The American video game developer also said it had not asked Formosa to cancel a previously registered game.

Known for its free-to-play structure and team collaboration, "League of Legends" is one of the most popular games in the world with one of the largest Esports competitions.

The League of Legends World Championship gives teams from around the globe the opportunity to compete for millions of dollars that are distributed among members.

This strike follows the union's recent gains with legal protections against artificial intelligence (A.I) for Hollywood performers signed by California Governor Gavin Newsom in September as well as a deal reached with major record labels such as Warner Music Group and Sony Music Entertainment in April.