A federal appeals court on Monday rejected Elon Musk's bid to modify or end his 2018 agreement with the U.S. Securities and Exchange Commission that required him to obtain prior approval from a Tesla Inc lawyer for some of his tweets.

The 2nd U.S. Circuit Court of Appeals in Manhattan rejected Musk's claim that the SEC has used his consent decree to conduct bad-faith, harassing investigations of his protected speech, and that the regulator's enforcement methods have made it substantially more onerous for him to comply.

Lawyers for Musk did not immediately respond to requests for comment. The SEC did not immediately respond to a similar request.

Musk's consent decree resolved an SEC lawsuit accusing him of defrauding investors with an Aug. 7, 2018, tweet that he had "funding secured" to take his electric car company private.

He and Tesla each also paid $20 million in civil fines, and Musk gave up his role as Tesla chairman.

In seeking to overturn the pre-approval mandate, Musk's lawyers called the restriction a "government-imposed muzzle" that chilled his speech on a wide range of topics.

However, the appeals court said Musk could have negotiated a settlement that preserved his unfettered right to tweet but chose not to, and had no right to revisit the matter "because he has now changed his mind."

(Reporting by Jonathan Stempel in New York; editing by Jonathan Oatis)