Apple has filed a lawsuit against Chinese smartphone giant Oppo, accusing the company of conspiring with a former Apple Watch engineer to steal confidential health-sensing technology.

The case centres on Chen Shi, a former sensor system architect at Apple. According to Apple’s complaint, Shi secretly accessed and downloaded sensitive documents related to the Apple Watch’s health sensors, including ECG, temperature and optical sensor technologies, in the weeks before leaving the company in June.

Apple alleges that Shi misled colleagues by claiming he was returning to China to care for his parents, while in fact preparing to take up a role at Oppo’s Silicon Valley research arm, InnoPeak.

Court filings say Shi held dozens of one-on-one meetings with Apple staffers outside his normal scope of work and, just three days before his departure, downloaded 63 protected files which were later copied onto a USB drive.

Further evidence cited includes messages allegedly sent by Shi to Oppo executives, in which he wrote that he was “collecting as much information as possible” before leaving Apple. Oppo’s vice president of health reportedly responded with approval.

Apple argues that Oppo not only knew about Shi’s activities but actively encouraged them, calling the conduct a serious threat to its multi-billion-dollar investment in wearable technology.

“Allowing this to go unpunished would undermine Apple’s commitment to innovation and provide a competitor with an unfair advantage,” the filing states.

Oppo has of course rejected the claims.

In a statement, the company said it “respects the trade secrets of all companies” and has “found no evidence establishing any connection between these allegations and the employee’s conduct during his employment at Oppo.” The company says it will cooperate with legal proceedings.

The lawsuit is the latest in a string of trade secret disputes involving Apple, which has previously accused former employees of funnelling sensitive information to Chinese firms.

Apple is seeking damages and an injunction to block Oppo from using the alleged stolen data.