With Meta’s new Threads app having picked up 30 million users on its first day, it’s little wonder Twitter is upset.

In fact, it’s so put out by Meta’s very similar app that it’s now threatening to sue the company, accusing it of violating Twitter’s intellectual property rights.

In a letter from Twitter to Meta chief Mark Zuckerberg that was first published by the news site Semafor, Musk lawyer Alex Spiro said that Twitter has “serious concerns that Meta has engaged in systematic, willful, and unlawful misappropriation of Twitter’s trade secrets and other intellectual property.”

It claimed that some of the “dozens” of former Twitter employees who now work for Meta have “improperly retained Twitter documents and electronic devices,” and that “Meta deliberately assigned these employees to develop, in a matter of months, Meta’s ‘copycat’ Threads app with specific intent that they use Twitter’s trade secrets and other intellectual property in order to accelerate the development of Meta’s competing app, in violation of both state and federal law as well as those employees’ ongoing obligations to Twitter.”

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

The letter added that Twitter has the right to take legal action “without further notice to prevent any further retention, disclosure, or use of its intellectual property by Meta.” But whether Twitter follows through with its threat remains to be seen.

Meta communications director Andy Stone hit back at the letter’s claims, saying on a Threads post that: “No one on the Threads engineering team is a former Twitter employee — that’s just not a thing.”

Elon Musk, who acquired Twitter in October for $44 billion, tweeted on Thursday: “Competition is fine, cheating is not.”

Recently appointed Twitter CEO Linda Yaccarino also got involved, tweeting: “We’re often imitated — but the Twitter community can never be duplicated.”

Asked on Threads if the new app could be more successful than Twitter, Zuckerberg said on Thursday: “It’ll take some time, but I think there should be a public conversations app with 1 billion-plus people on it. Twitter has had the opportunity to do this but hasn’t nailed it. Hopefully we will.”

Threads is off to a flying start for a couple of reasons. First, many Twitter users are upset by the constant disruptions and other issues that have plagued the platform since Musk bought the company last year. And second, Meta has built Threads with a direct link to the hugely popular Instagram app, making it easy to sign up and build an instant community.

Fancy giving Threads a go? Here’s how to get started.