Alec Radford, a key researcher in the development of OpenAI’s AI technologies, has received a subpoena in a copyright lawsuit against the AI startup, as revealed in a court filing on Tuesday.

The filing, submitted to the U.S. District Court in the Northern District of California by an attorney for the plaintiffs, indicates that Radford was served with the subpoena on February 25.

Radford, who left OpenAI at the end of last year to focus on independent research, was the primary author of OpenAI’s groundbreaking research paper on generative pre-trained transformers (GPTs), which form the basis of the company’s most popular products, including its AI-powered chatbot platform, ChatGPT.

Having joined OpenAI in 2016, a year after its founding, Radford worked on multiple models in the company’s GPT series, as well as Whisper, a speech recognition model, and DALL-E, the company’s image-generating model.

The copyright case, referred to as “re OpenAI ChatGPT Litigation,” was initiated by authors including Paul Tremblay, Sarah Silverman, and Michael Chabon, who claim that OpenAI infringed upon their copyrights by utilizing their work to train its AI models without proper authorization. The plaintiffs also argue that ChatGPT has infringed upon their works by extensively quoting them without providing attribution.

In the previous year, the Court dismissed two of the plaintiffs’ claims against OpenAI but allowed the claim of direct infringement to proceed. OpenAI maintains that its use of copyrighted data for training purposes is protected under the doctrine of fair use.

Radford is not the only prominent figure whose testimony is being sought by the authors’ attorneys. The plaintiffs’ lawyers have also filed a motion to compel the deposition of Dario Amodei and Benjamin Mann, former OpenAI employees who left the company to establish Anthropic. Amodei and Mann have resisted these motions, arguing that they are excessively burdensome.

A U.S. magistrate judge has ruled that Amodei must undergo hours of questioning regarding his work at OpenAI in two copyright cases, including a case filed by the Authors Guild.