An executive at artificial intelligence startup Stability AI resigned last week over the use of copyrighted material to develop AI tools — publicly taking sides in a debate that’s become central to the business model of the fast-growing industry.

Ed Newton-Rex, who was Stability’s vice president of audio, said Wednesday at the Cerebral Valley AI Summit in San Francisco that he left the company because he doesn’t believe that it’s legal to develop AI models using copyrighted content. Generative AI, one of the fastest-growing areas of artificial intelligence, functions by using vast swathes of data to train computers to generate content — like a poem, a song or an image — in response to a user’s prompt.