Twitter has threatened legal action against Meta over its new, text-based app called Threads, according to a letter obtained by Semafor.

In a Wednesday letter addressed to Meta CEO Mark Zuckerberg, Alex Spiro, an attorney representing Twitter, accused Meta of unlawfully using Twitter’s trade secrets and other intellectual property by hiring former Twitter employees to create a “copycat” app.

Since launching Threads Wednesday night, Meta’s new app has collected tens of millions of sign ups. The app, which was created by the company’s Instagram team, arrives at a time when many are looking for Twitter alternatives to escape Elon Musk’s raucous oversight of the platform since acquiring it last year for $44 billion.

Meta spokesperson Andy Stone responded to the report of Spiro’s letter on Threads Thursday afternoon, writing, “no one on the Threads engineering team is a former Twitter employee — that’s just not a thing.”

In the letter, which Semafor first reported on Thursday, Spiro said that Twitter “intends to strictly enforce its intellectual property rights” — and noted the company’s right to seek civil remedies or injunctive relief. He added that the letter marked a “formal notice” for Meta to preserve documents relevant for a potential dispute between the companies.

The Associated Press reached out to Spiro and Twitter on Thursday for further information. Twitter responded to an email seeking comment with a poop emoji, its standard automated response to reporters.

Musk hasn’t directly tweeted about the possibility of legal action, but he has replied to several snarky takes on the Threads launch. The Twitter owner responded to one tweet suggesting that Meta’s app was built largely through the use of the copy and paste function, with a laughing emoji.