Tesla Inc's Elon Musk on Thursday mocked the US Securities and Exchange Commission, just hours after a federal judge ordered him and the regulator to justify their securities fraud settlement, which let Musk remain chief executive. "And the name change is so on point!" he wrote.
In a letter to investors, David Einhorn, the manager of hedge fund Greenlight Capital, warned that investors should be very wary of Tesla stock.
After the now infamous tweet, shares in Tesla sunk over 2% just hours after sending it out on the social platform.
Here he's suggesting that the agency-whose mission is to protect investors from CEO misconduct-is actually harming the value of Tesla's stock by enforcing securities laws against Musk and Tesla.
The SEC said those claims were "false and misleading". Shares had already fallen 4.4 percent before the tweet to close at $281.83.
U.S. District Judge Alison Nathan in Manhattan said her regular practice is to have parties submit a joint letter, in this case by October 11, to show why their settlement was fair and reasonable and would not hurt the public interest.
The SEC declined to comment on Musk's tweet.
Murdoch, who owns roughly 10,000 shares of Tesla worth about $US3.03 million at Wednesday's price, also serves on the boards of Sky, TrueX Media, 21st Century Fox, New Corp, and Yankee Global Enterprises, as well as a handful of arts organisations, according to Bloomberg data.
Greenlight is having a hard year, with its main fund down 25.7 percent through September, but said its Tesla short position was its second biggest victor in the third quarter.
Tesla did not immediately respond to CNBC's request for comment.
Musk's sarcastic tweet could cause Nathan to reject the settlement if it gives her reason to believe that he "has no intention or ability to change his conduct", said Erik Gordon, a business professor at the University of MI.
Elon Musk's settlement with the SEC is not finalised yet. The SEC also alleged that Musk rounded up the buyout price for Tesla to US$420 a share to amuse his girlfriend at the time with a marijuana-culture reference.
Musk, for his part, has used Twitter to mock Einhorn, saying on August 1 he would "send Einhorn a box of short shorts to comfort him through this hard time".
Several sources also told the newspaper that Musk single-handedly prevented Tesla from reaching an earlier, more satisfactory settlement with the SEC.