Elon Musk and his brother are reportedly being investigated by the SEC over their recent stock sales.

• Elon Musk and his brother Kimbal Musk are being probed by the SEC for possible insider trading violations, according to a report by the Wall Street Journal on Thursday.
• Elon Musk's request for his followers to vote on whether he should sell some of his Tesla shares was preceded by a probe that focused on stock sales made by Kimbal Musk one day prior.

Insider trading rules may have been violated by recent stock sales made by CEO Elon Musk and his brother Kimbal Musk, who is a member of Tesla's board of directors, according to a report by the Wall Street Journal on Thursday, based on information from sources familiar with the matter.

Tesla's stock price briefly decreased due to the news but later increased by over 4% during the afternoon trading session.

An investigation by the SEC into stock sales by Kimbal Musk started last year and centers on transactions that took place one day before Elon Musk asked his followers on Twitter to vote on the future of his Tesla holdings.

The report was not commented on by the SEC, and Musk did not respond to a request for comment.

In an email exchange with CNBC on Tuesday, Musk mentioned an upcoming story about Tesla and the SEC that the Journal was reportedly working on.

Musk accused the SEC of leaking confidential information to the WSJ, which he claimed was a deliberate violation of federal law. He stated that he discovered this information because the WSJ inquired about it with Tesla before the SEC published it.

The SEC did not respond to CNBC's inquiry about Elon Musk's leak allegation, while the Wall Street Journal declined to comment on its sources for the story.

Elon Musk disclosed to CNBC his strained relationship with President Biden and encouraged the Justice Department's investigation of short sellers.

On November 6, 2021, Musk shared with his 62.5 million Twitter followers that he was considering selling 10% of his Tesla stock as a way to avoid tax on unrealized gains. He asked for their support, and 3,519,252 people responded, with 57.9% of them voting "Yes."

The day before his CEO brother's Twitter poll, Kimbal Musk disposed of approximately $109 million in shares, as per financial records.

On Monday, Elon Musk's Twitter poll resulted in a drop in stock shares.

Since late October 2021, they had been climbing, motivated by a strong 2021 third quarter and Hertz's announcement that it planned to order 100,000 Tesla vehicles for its fleet.

Elon Musk waited for a week after Hertz made its announcement to confirm that Tesla had not signed a contract with the rental car company yet. Prior to the confirmation, he teased investors who were short shares of Tesla on Twitter, writing: "Tesla Hertz shorts."

In Sept. 2021, Tesla CEO Musk stated that he was planning to sell a significant amount of his options in the fourth quarter, despite some fans believing they were providing him with advice on his stock sales through their Twitter poll votes.

He had to sell a significant portion of his shares to pay off his tax bill, as he stated.

According to public filings, most of the insider transactions by the Tesla chief and centibillionaire were part of a "Rule 10b5-1" trading plan dated Sept. 14, 2021, which allows company insiders to execute trades in their own company's stock for a set, future date.

In 2018, the SEC accused Musk of civil securities fraud, leading to a battle between Musk and the regulatory body. The two parties reached a revised settlement agreement in 2019 to resolve the charges.

The CEO of Tesla was not found guilty in the settlement, but had to give up his role as chairman of the board for three years.

The SEC has been accused of harassment by Musk due to its unrelenting investigation, which he claims is a form of retaliation for his public criticism of the federal financial regulators.

-- CNBC’s Brian Schwartz contributed reporting.