Writers Guild of America this week sent a letter to major Hollywood studios asking them to take action against tech companies that are using writers’ work to train AI tools without their permission.

“The studios, as copyright holders of works written by WGA members, have done nothing to stop this theft,” the guild’s leadership said in a letter. “They have allowed tech companies to plunder entire libraries without permission or compensation. The studios’ inaction has harmed WGA members.”

The guild said its collective bargaining agreement requires studios “to defend their copyrights on behalf of writers” and urged studios to “take immediate legal action against any company that has used our members’ works to train AI systems.”

The letter was sent to studios including Netflix, Warner Bros. Discovery, Walt Disney Co., Paramount Global, NBCUniversal, Sony Pictures and Amazon MGM Studios. Representatives from those studios either declined to comment or didn’t respond to requests for comment.

WGA’s letter referenced an Atlantic article last month that reported that subtitles from thousands of movies and TV episodes were included in an AI-training data set used by companies including Facebook parent company Meta and San Francisco-based AI company Anthropic. Anthropic and Meta did not immediately return a request for comment.

The WGA letter comes as some studios are in discussions with tech companies that are developing AI tools. In September, “Hunger Games” studio Lionsgate announced a partnership with AI startup Runway. Under that deal, Runway will create a new AI model for Lionsgate to help with behind-the-scenes processes such as storyboarding.

Other major Hollywood studios have yet to publicly announce deals, in part because AI is a complicated landscape where regulations and legal questions surrounding the technology are still evolving. There are also questions over how studio libraries should be valued for AI purposes and concerns about protecting intellectual property.