Another day, another tweet storm from Elon Musk that’s sent Tesla Inc. shares tumbling.

The stock dropped as much as 3.8 per cent as of 9:40 a.m. Friday in New York, after Musk fired off more than a dozen tweets targeting the Securities and Exchange Commission and short sellers the night before. He mocked the agency that he settled a lawsuit with only days earlier, referring to the regulator as the “Shortseller Enrichment Commission” and sarcastically quipping that it was “doing incredible work.”

The tweets may imperil a deal struck with the SEC on Saturday -- which isn’t final -- that bars Musk from serving as chairman of the carmaker for three years as punishment for problematic posts he sent about taking Tesla private. As part of the deal, the company also has to implement procedures and controls to oversee Musk’s communications, including his social media missives.

“At the very the least, they can read the riot act to Musk’s lawyer,” said Stephen Crimmins, a former SEC enforcement lawyer who’s now a partner at Murphy & McGovern. “Beyond that, if they feel he hasn’t lived up to his deal, they can theoretically seek to pull the settlement.”

Tesla shares are on track for their fourth consecutive daily decline and are down about 9.5 per cent this year.

Representatives for the Palo Alto, California-based company didn’t respond to requests for comment. Ryan White, an SEC spokesman, declined to comment.

The posts may test the boundaries of Musk’s agreement not to deny wrongdoing and risk reviving stiffer forms of punishment. Last week, the SEC sought to prohibit him from serving as an officer of a public company. A federal judge still has to decide whether the penalties levied against the CEO are appropriate.

“Reading the mind of Elon Musk is beyond my ability, but he is soon to join the SEC in front of a federal judge to defend the recent settlement agreement,” said Stephen Diamond, an associate professor of law at Santa Clara University, who specializes in corporate governance. “If he doesn’t want to put that deal at risk, he ought to pay attention to cars instead of Twitter.”

Musk also dragged BlackRock Inc. into his long-running dispute with short sellers, claiming that the fund manager was reaping heavy profits by lending shares they hold to this group of investors. Representatives for BlackRock in London weren’t immediately available for comment. The company held about 3.8 percent stake in Tesla as of the end of June, according to data compiled by Bloomberg.

It all started on Thursday at 4:16 p.m. New York time with a tweet that’s racked up more than 29,000 likes and 4,400 retweets:

The SEC, whose @SEC_News Twitter handle has about 251,000 followers to Musk’s more than 22.8 million, is also active on the messaging service but has refrained from posting about Musk or Tesla since last weekend’s settlement.

The agency accused Musk in its Sept. 27 complaint of misleading investors with his infamous Aug. 7 tweets about having the investor support and “funding secured” to take Tesla private.

In court papers and at a news conference, the regulator went to great lengths to spell out Musk’s carelessness and erratic behavior, highlighting his threat earlier this year to “burn” investors betting against Tesla stock. 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 agreed in the settlement to pay a US$20 million fine. Tesla was hit with the same penalty and has to add two new board members, plus appoint an independent chairman.

“I’m shocked,” Charles Elson, director of the John L. Weinberg Center for Corporate Governance at the University of Delaware, said of Musk’s attack on the agency. “It’s only inviting the SEC to rethink the settlement. And it’s going to make it much tougher to attract independent directors to join the board.”