Billionaire businessman Elon Musk on Thursday asked the US Supreme Court to consider whether the Securities and Exchange Commission overstepped its authority in enforcing a consent decree that he has called a “muzzle” on his constitutional free speech rights, his lawyer said.

Musk asked the justices to hear his appeal of a lower court’s decision in May that upheld the decree, which arose from his August 2018 post on the social media platform then called Twitter, now called X, that he had “funding secured” to take his electric car company Tesla private, his lawyer said.

A three-judge panel of the Manhattan-based 2nd US Circuit of Appeals rejected Musk’s claim that the SEC, which accused him of defrauding investors, exploited the decree to conduct harassing investigations into his use of Twitter.

Musk bought the social media platform last year and renamed it.

The consent decree was part of a settlement with the SEC under which Musk and Tesla each paid $20 million fines, Musk gave up his role as Tesla’s chairman and he agreed to let a Tesla lawyer approve some Twitter posts in advance.

In its ruling, the three-judge panel said Musk could not revisit the screening of Twitter posts because he had “changed his mind.”

The 2nd Circuit in July denied Musk’s request to rehear the case.

Musk’s lawyers have said the SEC had no right to impose, as a condition of settling, a “gag rule” that they contend violated the Constitution’s First Amendment constraints on governmental limits on free speech.

Separately, the New Orleans-based 5th US Circuit Court of Appeals has agreed to reconsider its March decision that Musk violated federal labor law by posting on Twitter in May 2018 that Tesla employees would lose stock options if they joined a union.

The 5th Circuit is set to hear arguments in the case in January.