The U.S. Securities and Exchange Commission (SEC) has taken legal action against billionaire Elon Musk, accusing him of not promptly revealing his ownership of Twitter stock prior to his acquisition of the social media platform in early 2022.

The SEC’s allegations suggest that this failure to disclose allowed Musk to pay “at least $150 million” less than he should have for shares. Musk officially purchased Twitter in October 2022, subsequently rebranding it as X.

Musk began acquiring shares of Twitter in early 2022, and by March, he owned more than 5% of the company. According to the SEC’s complaint, he was legally obligated to announce his ownership at that point but did not actually disclose it until April 4, which was 11 days after the deadline.

In response to the lawsuit, Musk’s legal counsel, Alex Spiro, claimed that the SEC’s actions indicated its inability to formulate a genuine case, as Musk had not committed any wrongdoing. He referred to the lawsuit as a “sham.”

Spiro also noted that “the SEC’s multi-year campaign of harassment against Mr. Musk culminated in the filing of a single-count technical complaint against Mr. Musk under Section 13(d) for an alleged administrative failure to file a single form—an offense that, even if proven, incurs only a nominal penalty.”

After Musk reached an agreement to buy Twitter in April 2022, he attempted to retract his commitment, prompting the company to take legal measures to enforce the deal.

Since April 2022, the SEC has been conducting an investigation to ascertain whether any securities regulations were violated concerning Musk’s Twitter stock purchases, as well as related statements and filings he made with the SEC.

Before proceeding with the lawsuit, the SEC sought a court order to require Musk to provide testimony as part of its examination of his Twitter acquisition.

With the current SEC chair, Gary Gensler, set to resign from his position on January 20, it remains uncertain whether the incoming leadership will choose to pursue the lawsuit further.