Elon Musk, Tesla’s chief executive, was accused by federal regulators on Thursday of misleading investors with false public statements, a move that could force him out of the company’s leadership.
At issue is Mr. Musk’s declaration on Twitter last month that he had “funding secured” to buy out the stock of the electric-car maker. The prospect created a firestorm on social media and in the markets that sent Tesla’s shares soaring.
In a lawsuit filed in federal court in New York, the Securities and Exchange Commission accused Mr. Musk of committing fraud by making false public statements with the potential to hurt investors.
The suit seeks to bar Mr. Musk, who is also Tesla’s chairman, from serving as an executive or director of publicly traded companies like Tesla. Such a punishment is one of the most serious remedies the S.E.C. can impose against a corporate executive.
The case is likely to send shock waves across corporate America and could lead to a re-evaluation of how companies use Twitter to communicate with the investing public.
The S.E.C. said Mr. Musk “knew or was reckless in not knowing” that his statements were false or misleading. “In truth and in fact, Musk had not even discussed, much less confirmed, key deal terms, including price, with any potential funding source,” the S.E.C. said in its lawsuit.
In a statement distributed by Tesla, Mr. Musk said: “This unjustified action by the S.E.C. leaves me deeply saddened and disappointed. I have always taken action in the best interests of truth, transparency and investors. Integrity is the most important value in my life and the facts will show I never compromised this in any way.”
The S.E.C. approached the Tesla chief with an offer to settle the case, according to a person familiar with his thinking, but he refused to negotiate, adamant that he had done nothing wrong. A person briefed on the talks said they fell apart Thursday morning, setting the stage for the S.E.C. to vote on the action.
Tesla itself was not named as a defendant.
A Silicon Valley veteran who joined in founding the company 15 years ago, Mr. Musk is widely regarded by analysts and investors as the creative engine behind Tesla. It has become the most valuable American carmaker, with its stock worth more than $50 billion.
The shares tumbled more than 12 percent in after-hours trading after the S.E.C. filed its lawsuit.
Twitter has been a frequent outlet for Mr. Musk, who posted on Aug. 7 — while he was driving himself to the airport in a Tesla Model S — that he was “considering taking Tesla private at $420.”
It soon emerged that Tesla’s board members were blindsided by Mr. Musk’s post. Tesla at the time hadn’t hired investment banks or others to help raise the money that would be needed to take the company private. And many Tesla investors — natural places to seek financing — said they hadn’t heard anything from Mr. Musk before his tweet.
The S.E.C. issued a round of subpoenas to Tesla and the financial institutions it eventually hired for advice on a potential conversion into a private company. The agency also interviewed a number of Tesla board members, according to a person with knowledge of the matter.
The complaint said Mr. Musk “knew that he had never discussed a going-private transaction at $420 per share with any potential funding source.”
The S.E.C. said that Mr. Musk had been in a persistent feud with investors who were betting that Tesla shares would fall. The complaint notes that Mr. Musk had discussions in late July with a foreign investment fund that had recently acquired a 5 percent stake in Tesla. In those discussions, Mr. Musk said he was thinking about taking Tesla private, but regulators said nothing formal was agreed on.
The lawsuit is the latest in a series of escalating problems for Tesla and Mr. Musk. The company has been struggling to achieve the ambitious production targets that Mr. Musk had publicly outlined. He has made a series of unusual public comments or appearances, including an internet interview in which Mr. Musk appeared to smoke marijuana.
The action by the S.E.C. is solely related to events surrounding Mr. Musk’s comments on Twitter. But regulators had been investigating Tesla even before the tweet, and are more broadly examining whether Tesla misled investors about its production goals.
Federal prosecutors in California have also sought information from Tesla, an inquiry that appears to be at an early stage.
Tesla’s directors issued a statement affirming that they are “fully confident in Elon, his integrity and his leadership of the company.”
The action against Mr. Musk, 47, is one of the most significant by the S.E.C. during the Trump administration, which has been criticized for focusing on smaller cases. The agency seldom tries to bar a figure as prominent as Mr. Musk permanently from the securities industry.
When S.E.C. lawyers accused the billionaire Mark Cuban of insider trading in 2008, for example, they did not seek such a ban. Mr. Cuban won the case at trial. When they settled a case against the hedge fund manager Steven A. Cohen for failing to supervise his $13 billion hedge fund, SAC Capital, where several portfolio managers were charged with insider trading, the S.E.C.’s lawyers required Mr. Cohen to stop managing investors’ money only for a period of two years.
Even Elizabeth Holmes, chief executive of the defunct medical company Theranos, who is now facing criminal charges of defrauding investors, did not receive a permanent industry ban. In a settlement with the S.E.C. over the claims made for the company’s blood-testing equipment, she agreed not to serve as a director or officer of a public company for 10 years.
“This case demonstrates our commitment to holding individuals accountable for violations,” said Steven Peikin, the S.E.C.’s co-director of enforcement. “Neither celebrity status nor reputation as a technological innovator provide exemptions from the securities laws.”
The S.E.C. complaint is quite detailed in describing the events that led to Mr. Musk’s fateful tweet.
The filing said that on Aug. 2, five days before he sent the tweet, Mr. Musk sent an email to Tesla’s board, chief financial officer and general counsel with the subject line: “Offer to Take Tesla Private at $420.” Mr. Musk said he wanted to put the matter up to a shareholder vote “at the earliest opportunity,” the complaint added, and wanted to do so partly because of the attacks on the company’s stock from bearish investors known as short-sellers.
Mr. Musk, according to the lawsuit, told Tesla’s board that the $420 figure was based on a 20 percent premium to the stock’s Aug. 2 closing price. He then rounded it up to $420 after his girlfriend told him of the number’s significance for marijuana smokers and thought it would be funny.
The board on Aug. 3 authorized Mr. Musk to start talking to some investors about the plan to go private and asked him to report back on those conversations, the complaint said. Mr. Musk had a conversation with at least one large investor, it added, but before anything was close to completion, he began posting statements on Twitter about taking the company private on Aug. 7.
The S.E.C. said that in the ensuing days, Mr. Musk did nothing to clarify his statements and threw fuel on the fire with additional posts on Twitter.
The case against Mr. Musk is noteworthy also for the speed with which the S.E.C. brought it. Rebecca Roiphe, a professor at New York Law School, said the case was “done in record time,” adding, “Usually there is much more opportunity for the defendant to be heard and make formal submissions.”
Michael Liftik, a lawyer with Quinn Emanuel Urquhart & Sullivan and a former S.E.C. attorney who helped write the commission’s policy on social media posts, said the investigation was most likely straightforward.
“It was one tweet — it is one sentence,” Mr. Liftik said. “‘Funding secured’ is a definitive declarative sentence and it didn’t leave him any wiggle room.”
The S.E.C. policy, adopted in 2013, permits a corporation to disclose market-moving information on Twitter as long as it has given investors advance notice that it may do so. Tesla had done that and said Mr. Musk’s Twitter account is one place the company might make significant corporate announcements.
The episode arose as Mr. Musk had made a priority of smoothing out the assembly of a crucial new product, the Model 3 roadster. In a bid to lift output to 5,000 vehicles a week, he stalked around the plant in Fremont, Calif., joining in to help solve bottlenecks and other problems and sometimes sleeping on the factory floor.
Cash has also been a problem for Tesla. Besides spending to ramp up Model 3 production and develop future vehicles, Tesla faces two significant bond payments that could put further stress on its reserves. Most analysts believe Tesla will have to raise additional capital from investors to meet those obligations, but Mr. Musk has said it has no plans to do so.
In recent months, as he has juggled Tesla’s production and financing demands, there has been talk about installing a chief operating officer to enable Mr. Musk to take a reduced role in day-to-day operations. But there has been no sign of any active search, and there is no evident internal candidate for such a role.
While Model 3 production has accelerated significantly this year, it is unclear how smoothly the process is running. Some owners have complained that cars arrived with crooked panels and other flaws. Hundreds of Model 3s have been parked in lots around California and other states, some needing repairs before they can be delivered.
Neal E. Boudette and David Gelles contributed reporting.