Apple is not playing around with its lawsuit against OpenAI, its onetime partner and now apparent rival, over allegedly stolen trade secrets. After filing a bombshell lawsuit against the AI company last week, the Cupertino giant has reportedly sent legal letters to roughly 40 former employees who now work at OpenAI. The Financial Times reports, citing unnamed sources, that the letters direct the former employees to preserve relevant documents and communications and ask them to meet with Apple’s lawyers. The outlet describes the move as part of an aggressive strategy by Apple to gather evidence supporting its case. OpenAI and Apple did not immediately respond to requests for comment. The letters are a major escalation in a legal battle that could throw a wrench into OpenAI’s closely watched plans to get into the consumer hardware game.

Apple filed its lawsuit in California federal court last week, accusing OpenAI and two former Apple employees who now work at the AI company of stealing trade secrets related to Apple’s manufacturing processes and products still in development.

Apple’s complaint alleges that OpenAI Chief Hardware Officer Tang Tan, a former Apple vice president, directed Apple employees interviewing with OpenAI to share company secrets during the hiring process. Tan is named as a defendant in the suit. The suit represents an existential crisis for OpenAI’s plans as a hardware business. Apple argues that OpenAI’s future products would be fundamentally built on stolen property. “He has directed job candidates still working for Apple to bring ‘Actual parts’ from Apple to their interviews for ‘show and tell’ sessions in which he and his team at OpenAI can elicit still more Apple confidential information,” the lawsuit states.