Elon Musk reportedly faces a Federal Trade Commission probe into whether he violated federal disclosure rules while amassing an approximately 9% stake in Twitter – a move that preceded his blockbuster $44 billion takeover of the social media giant.

The feds are examining whether Musk erred under the Hart-Scott-Rodino Act, a 1976 antitrust provision requiring investors to provide a “pre-merger notification” to the FTC and the Justice Department. The law applies for active investors who acquire large stakes in a company.

Musk, who began buying Twitter shares on Jan. 31, initially disclosed his stake in the company in an April 4 filing that classified him as a passive investor.

The billionaire refiled the disclosure one day later to reflect that he was an active investor after he publicly engaged with Twitter’s board about potential changes at the company.

The FTC wants to review communication between Musk and Twitter’s board as it assesses whether he bought shares with plans to play an active role in the company’s activities, The Information reported, citing sources familiar with the matter.

Musk could face fines if the FTC’s probe determines he violated the Hart-Scott-Rodino Act by failing to properly disclose his investment, according to the report. However, the fine would amount to a maximum of $46,517 per each day Musk failed to adhere to guidelines – a paltry sum for the world’s richest individual.

FTC officials did not immediately return a request for comment on the report.

Musk’s initial disclosure of his Twitter share purchases immediately drew scrutiny from regulatory experts earlier this month – some of whom noted that the billionaire missed the SEC’s reporting deadline by several weeks when his stake in the company surpassed 5%.

Musk exceeded the threshold on March 14, but his stake wasn’t publicly revealed until early April – meaning the broader market was unaware and share prices did not react to his investment.

The SEC has yet to publicly say if Musk is under scrutiny for that apparent misstep.

While Musk’s personal transactions are under review, antitrust regulators aren’t expected to block his $44 billion Twitter deal.

As The Information noted, Twitter has little overlap with Musk’s other business interests, such as Tesla, SpaceX and The Boring Company. However, the FTC is chaired by antitrust crusader Lina Khan, who has signaled a crackdown on major tech deals and mergers.

Federal Communications Commissioner Brendan Carr, the panel’s senior Republican, called suggestions that the FCC could block the deal “absurd.”