The lawsuit marks the latest salvo in a years-old feud between the SEC and Musk, who has become one of the regulator's highest-profile critics.

Twitter's stock price rose 27 percent once Musk belatedly disclosed his stake, the lawsuit said. "During the period that Musk was required to publicly disclose his beneficial ownership but had failed to do so, he spent more than $500 million purchasing additional shares of Twitter common stock," it said.

The SEC alleges Elon Musk violated federal securities law by failing to disclose his more than 5% stake in Twitter on time.

Musk, who bought Twitter in October 2022 and renamed it X, had started amassing shares earlier that year. His ownership amounted to more than 5% by March, requiring him to file a disclosure report. The SEC says the report was 11 days late, allowing Musk to "underpay by at least $150 million” for shares purchased before he disclosed his stake.

Elon Musk is only one week into his role in President Donald Trump’s new administration, but the US federal government is already rolling out the Twitter playbook to manage its spending and personnel.

Elon Musk, the genius billionaire behind Tesla, SpaceX, and now the Department of Government Efficiency (D.O.G.E), has vowed to cut wasteful spending in Washington under his “best friend” President Donald Trump’s administration.

Donald Trump’s administration has been hit with a lawsuit over allegedly collecting federal employee information and directing it to an employee of Elon Musk. The lawsuit, filed in the U.S. District Court for the District of Columbia Monday,