The Securities and Exchange Commission waged another legal battle against Tesla ( TSLA ) CEO and X owner Elon Musk, this time accusing the billionaire of defrauding Twitter’s shareholders.

In a lawsuit filed in a Washington, D.C., federal district court Tuesday, the SEC accused Musk of flouting commission rules designed to protect shareholders during his 2022 takeover bid for the social media company.

“Musk failed to timely file with the SEC a beneficial ownership report disclosing his acquisition of more than 5% of the outstanding shares of Twitter’s common stock in March 2022, in violation of the federal securities laws,” the SEC said in its complaint.

The commission alleged that Musk’s untimely filing kept Twitter shares at artificially low prices, during which he purchased additional shares. The late filing allowed Musk to purchase the shares for at least $150 million less than what they were worth, the SEC said.

Under SEC rules, investors who acquire more than 5% of a company’s registered voting equity shares must disclose the position to the commission within 10 days. The rule is intended to ensure that other stakeholders have an opportunity to evaluate their own positions and buy or sell shares as they see fit.

Musk began acquiring Twitter shares in January 2022. By March 14 that year, his stake had exceeded 5% ownership in the company. Musk missed the SEC’s first filing deadline on March 24 and in a late filing on April 4 designated himself as a passive investor.

“That day, Twitter’s stock price increased more than 27% over its previous day’s closing price,” the SEC alleged.

The commission said Musk not only disclosed his Twitter position too late but also falsely held himself out as a passive investor, rather than as an active investor intending to exert control over the company. By withholding those facts from shareholders, the SEC alleged, Musk committed securities fraud.

Musk refiled his disclosure as an active investor the next day on April 5.

The lawsuit comes in the final days of the commission’s leadership under SEC Chair Gary Gensler, who, like his predecessor Jay Clayton, has investigated Musk's financial dealings.

Clayton targeted Musk over a 2018 post to Twitter saying he had “funding secured” to take Tesla private. The claim led to an SEC lawsuit against Musk that ended in a settlement .

Gensler launched the SEC's investigation into Musk's Twitter share acquisitions and disclosures in April 2022. Whether Musk will need to defend the lawsuit will depend on the will of the SEC under new leadership. Gary Gensler's term as SEC chair expires Jan. 20. And President-elect Trump nominated former SEC Commissioner Paul Atkins to lead the agency.

The same month the SEC launched its investigation, a Twitter shareholder sued Musk over the same disclosures, alleging that his filings with the SEC came six trading days too late, during which Musk unfairly bought 15 million of 56 million Twitter shares traded during the six-day period.

By the time Musk publicly availed his position, the shareholder claimed, Musk had acquired a 9.2% stake that allowed him to save $143 million on his purchase of Twitter shares.

“At a minimum, he profited $150 million against the backs of common shareholders,” Jacob Walker, an attorney for the shareholder, told Yahoo Finance in April 2022.

The shareholder lawsuit is pending in federal district court in New York's Southern District.

In a court document Musk filed in that case, he described his delinquent SEC filings as a "mistake," an important distinction for his defense, which will depend on whether or not a jury accepts that he did not intend to defraud Twitter shareholders.

Musk, meanwhile, has shot back at the SEC on X, calling the commission a ”totally broken organization.”

Musk's lawyer Alex Spiro sent a letter to the SEC Chair Gary Gensler in December rejecting what he said was an offer from the commission demanding to settle its Twitter disclosure complaints. Multiple news outlets said Spiro called the SEC's lawsuit a "sham" and said his client had done nothing wrong.

The SEC in its complaint asked for the court to order Musk to pay back his "unjust enrichment" as a result of his alleged violation, as well as civil penalties.

Alexis Keenan is a legal reporter for Yahoo Finance. Follow Alexis on X @alexiskweed .