Twitter has sent a letter to Meta Platforms, the parent company of Facebook, threatening to sue them over their new Threads platform. The letter, written by Twitter’s lawyer Alex Spiro and addressed to Meta CEO Mark Zuckerberg, accuses Meta of hiring former Twitter employees who have access to Twitter’s trade secrets and highly confidential information.

The news was first reported by the website Semafor, and a Reuters source has confirmed the contents of the letter. However, Spiro did not respond to a request for comment from Reuters. In the letter, Spiro states that Twitter intends to strictly enforce its intellectual property rights and demands that Meta immediately cease using any Twitter trade secrets or highly confidential information.

Meta, which recently launched Threads and has already garnered more than 30 million sign-ups, aims to take on Elon Musk’s Twitter by leveraging the massive user base of Instagram, which is also owned by Meta. However, Meta’s spokesperson, Andy Stone, refuted the accusations in a Threads post, stating that none of the engineering team members for Threads are former Twitter employees.

A former senior Twitter employee, speaking to Reuters, stated that they were not aware of any former Twitter staffers working on Threads or joining Meta. Meanwhile, Elon Musk, the owner of Twitter, responded to the news with a tweet stating, “Competition is fine, cheating is not.”

Intellectual property law experts, including Stanford law professor Mark Lemley, suggest that for Twitter to press a trade secret theft claim against Meta, they would need more substantial evidence than what is provided in the letter. Merely hiring former Twitter employees and creating a similar site is unlikely to support a trade secrets claim. Companies making such allegations must demonstrate that they made reasonable efforts to protect their corporate secrets.

The potential legal challenge from Twitter comes amid a series of controversial decisions by the platform that have led to user and advertiser dissatisfaction. Elon Musk’s recent decision to limit the number of tweets users can read per day has added to the criticism surrounding Twitter’s actions.