US market regulators are probing whether Tesla boss Elon Musk and his brother violated insider trading rules in connection with whopping share sales last year, the Wall Street Journal reported Thursday.
According to the report, the investigation began last year after his brother Kimbal sold shares of the electric carmaker valued at $108 million, a day before Musk polled Twitter users asking whether he should offload 10% of his stake in Tesla.
Kimbal Musk did not know about the Twitter poll ahead of it, however Elon Musk told the Financial Times in an email, adding that his lawyers were "aware" of the poll.
The probe is looking into whether Elon Musk told his brother, also a member of the Tesla board of directors, that he would post the tweet and whether Kimbal Musk then traded, the Journal reported.
An earlier settlement with the SEC required his public statements about the company's finances and other topics to be vetted by its legal counsel.
The SEC issued a subpoena on November 16, ten days after Musk's poll, seeking information related to some financial data.
The potential probe would escalate Musk's battle with regulators as they scrutinize his social media posts and Tesla's treatment of workers, including accusations of discrimination.
Last week, Musk accused the SEC of harassing him and Tesla with an "endless" and "unrelenting" investigation to punish him for being an outspoken critic of the government.
Elon Musk's share sales in November were automatically executed according to a trading plan he had created on September 14, showed a filing disclosing share sales, including stock options that were supposed to expire in 2022.
Tesla's stock has fallen about 33% since Musk began selling billions of dollars worth of shares on November 8, few days after the poll where 58% of voters asked him to sell.
Tesla and Kimbal Musk did not immediately respond to Reuters' requests for comment. A spokesperson for the SEC declined to comment.