Fox has sent Tucker Carlson a “cease and desist” letter over videos he says he posts on Twitter, in an escalation of tensions between the right-wing media star and his former employer.

Carlson was one of the most popular anchors on Fox News before being abruptly fired in April, in the wake of the company’s $787.5 million settlement with polling company Dominion over the network’s role in spreading conspiracy theories about voter fraud . His departure has shaken up a conservative media landscape in the US, which has long been dominated by Fox.

He announced plans to relaunch his show on Twitter last month, a point of contention with Fox as the two sides battle over the details of his contract. According to Carlson’s lawyers, any non-compete clause was no longer valid because Fox had previously breached its contract.

Harmeet Dhillon, an attorney representing Carlson, said, “Fox is doubling down on the most catastrophic programming decision in cable news industry history and is now demanding that Tucker Carlson remain silent until after the 2024 (U.S.) election.”

Fox News did not respond to a request for comment.

Carlson posted two “episodes” to Twitter last week, which consisted of monologues of about 10 minutes each.

Last month, he alluded to his departure from Fox, warning his followers on Twitter that journalists at established media groups face limits and that breaking them too often leads to dismissal.

He said: “What is it like to work in such a system? After being in the middle of it for over 30 years, we could tell you stories. The best you can hope for in the news world right now is the freedom to tell the fullest truth you can.

“But there are always limits. And you know that if you hit those limits often enough, you get fired for it,” he added.

Fox fired Carlson in part because of private messages he sent, which have been made public in legal documents in recent months, according to people who knew about his departure. Some reports indicated that Carlson was critical of Fox’s management.