In what may be the clearest sign yet that Twitter sees Meta as a competitive threat, the former has threatened the latter with a lawsuit following the successful launch of Meta's new Twitter rival, Threads.

An attorney for Twitter on Wednesday sent a letter to CEO Mark Zuckerberg accusing Meta of stealing trade secrets by employing former Twitter employees.

In a letter, Alex Spiro, an outside lawyer for Twitter owner Elon Musk, claimed that Meta had committed "systematic, willful, and unlawful misappropriation of Twitter's trade secrets and other intellectual property."

In response to reports on the letter, Musk tweeted: "Competition is fine, cheating is not."

The letter goes on to say that Meta hired former Twitter employees who "have improperly retained Twitter documents and electronic devices" and that Meta "deliberately" involved these employees in developing Threads.

"Twitter intends to strictly enforce its intellectual property rights," Spiro said, adding, "and demands that Meta take immediate steps to stop using any Twitter trade secrets or other highly confidential information."

The letter was dismissed by Meta spokesperson Andy Stone.

"No one on the Threads engineering team is a former Twitter employee -- that's just not a thing," he said on Threads, as per CNN.

Since Musk paid USD 44 billion to buy Twitter, the social network has faced competition from an increasing number of smaller microblogging sites, including the decentralized social network Mastodon and Bluesky, a rival supported by former Twitter CEO Jack Dorsey. However, Twitter has not indicated that it will file a lawsuit.

Unlike some Twitter competitors, Threads has grown quickly, and, according to Zuckerberg, 30 million users signed up for the app on its first day. Threads was the number-one free app on the iOS App Store as of Thursday afternoon.