A U.S. financial regulator is suing Elon Musk, saying he failed to disclose his ownership of Twitter stock and then angered other shareholders by acquiring the company's shares at an "artificially low price."

The U.S. Securities and Exchange Commission (SEC) filed a lawsuit against Musk in federal court in Washington, D.C., on Tuesday night, accusing him of securities violations. According to the lawsuit, Musk failed to disclose that he had promptly acquired a 5% stake in the company, causing him to "underpay at least $150 million for the stock purchased after the financial beneficial ownership report was due."

Musk acquired Twitter for $44 billion in 2022 and later renamed it X. Prior to the purchase, Musk purchased a 5% stake in the company, which typically requires public disclosure. The SEC said Musk did not disclose his ownership in Twitter until 11 days after the report was due.

Alex Spiro, Musk's attorney, said in an emailed statement that the SEC's case amounts to an "admission" that the agency does not have any case. Spiro said Musk "did nothing wrong and everyone saw this scam for what it was."

This is not the first time the SEC has investigated Musk's acquisition of Twitter. The agency launched an investigation into Musk and his brother Kimbal Musk in 2021, accusing them of securities fraud and violating insider trading rules after selling tens of thousands of Tesla shares. Musk is Tesla's CEO and his brother is a board member.

Spiro said the SEC lawsuit resulted from the administration's failure to "file a single form." He added that "the SEC has engaged in a multi-year harassment campaign against Mr. Musk, culminating in the filing of a single-alleg thorny complaint against Mr. Musk."

Over the past few months, Musk has developed a close relationship with Donald Trump. Musk has donated millions of dollars to his re-election campaign and campaigned with him. Trump has since appointed Musk as the head of an advisory group he said he would create, called the "Department of Government Effectiveness," to oversee government regulations and spending.

The SEC said in the lawsuit that before Musk delayed disclosing his ownership stake in Twitter, he allegedly spent more than $500 million to buy additional stock in the company and was able to steal money from unsuspecting people at "artificially low prices." of the public to buy the stock.

When Musk finally disclosed his ownership to the SEC 11 days later, he said he had purchased more than 9% of Twitter stock. "On that day, Twitter's stock price rose more than 27% from the previous day's closing price," the SEC wrote in the lawsuit.