Twitter’s lawyer wrote a letter to Facebook parent Meta on Wednesday, accusing the company of “systematic” and “unlawful misappropriation” of trade secrets following the launch of its Threads service.

The letter from longtime Elon Musk attorney Alex Spiro alleged that Meta’s new Twitter clone was built by former Twitter employees “deliberately assigned” to develop a “copycat” app. Semafor was first to report on the letter.

Spiro offered no concrete examples of Twitter employees using trade secrets to build the app, which notched millions of users within hours of its launch. But the message — sent on same day that Threads opened to the public — shows Musk’s level of concern given Meta’s userbase and technical capacities.

“No one on the Threads engineering team is a former Twitter employee,” Andy Stone, Meta communications director, posted on Threads. “That’s just not a thing.”

Since Musk’s $44 billion purchase of Twitter in October, the site has been riddled with challenges, including some advertisers suspending their campaigns. Musk has dramatically downsized the company, leaving it slow to respond to glitches.

Spiro said Meta is “expressly prohibited” from crawling or scraping Twitter’s follower data, without providing evidence that Meta has engaged in that activity. Musk previously alleged that scraping of Twitter user data occurred on a large scale, though he, too, neglected of show specific examples.

On Thursday, Twitter’s new CEO Linda Yaccarino tweeted that the company was “often imitated,” a clear reference to Threads.

Threads has already launched with representation from major brands and celebrities. The app still lacks some critical features, including a web app, and isn’t yet generating revenue.

WATCH: Threads’ speed of growth has been absolutely breathtaking