Apple on Friday accused OpenAI of stealing secrets about products still in development, setting up a legal face-off between two of the world’s biggest tech companies.

In a lawsuit filed in U.S. District Court for the Northern District of California, the consumer tech giant said that OpenAI, a leader in artificial intelligence that has a new hardware business, had asked job candidates from Apple to share details about secret projects and to bring device components and prototypes to their interviews.

Apple also accused an OpenAI employee of downloading internal documents from a laptop owned by the iPhone maker.

OpenAI used the confidential information to approach Apple’s manufacturing partners, including asking one partner to demonstrate Apple’s technique for finishing metal on its devices, the lawsuit says.

Apple sent a letter to OpenAI in February to raise concerns that confidential information could be “making its way to OpenAI’s business improperly,” according to the suit. OpenAI did not respond, Apple said.

“OpenAI’s nascent hardware business now rests on the shakiest of foundations, rotten to its core by its illegal reliance on misappropriated trade secrets,” Apple wrote in its lawsuit.

OpenAI did not immediately respond to a request for comment.

(The New York Times has sued OpenAI and Microsoft, claiming copyright infringement of news content related to A.I. systems. The two companies have denied those claims.)

Apple’s lawsuit against OpenAI adds to a souring partnership between the tech titans. Apple has largely remained on the sidelines of A.I., even as other technology giants spend hundreds of billions of dollars building A.I. models and data centers and as start-ups push the envelope on the technology.

To help catch up, Apple struck a deal with OpenAI in 2024 to use the A.I. start-up’s technology to overhaul its products, including its digital assistant Siri. But OpenAI grew disappointed by how Apple integrated ChatGPT, and has even considered legal action. In January, Apple said it was partnering with Google to power Siri and its other A.I. products.

Adding to the tension, OpenAI, which has confidentially filed for an initial public offering, is creating a new family of hardware products itself.

OpenAI last year paid $6.5 billion to buy IO, which at the time was a one-year-old design studio founded by Jony Ive, Apple’s former longtime design head. Engineers and designers have steadily departed Apple for OpenAI since the deal.

In its lawsuit Friday, Apple accused Tang Tan, OpenAI’s chief hardware officer and a former Apple executive, of coaching his hires from Apple on how to evade Apple’s security processes for departing employees.

Mr. Tan did not immediately respond to a request for comment.

Apple accused another former employee, Chang Liu, of using a former colleague’s Apple-owned laptop to access and download technical documents while working at OpenAI. Mr. Liu told that Apple employee what information about unannounced products she should study before job interviews, Apple said.

Mr. Liu also planned to access internal documents through an Apple-owned laptop that he didn’t return when he left the company, according to the lawsuit.

Mr. Liu did not immediately respond to a request for comment.

OpenAI had misled the manufacturing company it approached to learn about the metal finishing technique to believe it had Apple’s permission to view it, according to the lawsuit.

Apple is seeking an injunction that would prevent OpenAI from possessing, using or sharing Apple’s trade secrets, as well as an order requiring OpenAI to return Apple’s intellectual property.