NEW YORK (AFP) - Twitter's new buyer Elon Musk still must have his tweets about his electric car company Tesla pre-approved, after a US judge on Wednesday (April 27) rejected an appeal to free him from oversight.

Musk last month filed a motion to overturn Securities and Exchange Commission (SEC) restrictions imposed following his 2018 tweet, in which he said he had acquired funding to take Tesla private, but did not provide proof or file paperwork with the securities regulator.

The tweet, which caused share prices to fluctuate wildly, was ruled to be "false and misleading" and shareholders have accused Tesla of securities fraud.

The SEC also charged Musk with fraud and ordered him to step down as chair of Tesla's board of directors, pay a US$20 million fine and, after another unfortunate tweet in early 2019, demanded his tweets directly related to business of the company be pre-approved by a competent lawyer.

Musk said he was forced to agree to the deal, and denies lying to shareholders.

However, "Musk's claim that he was the victim of economic duress is wholly unpersuasive," Judge Lewis Liman wrote in his ruling.

The judge said Musk's argument that the SEC has used the agreement "to harass him" and investigate his speech is "meritless" and "particularly ironic," since free speech rights do not allow him to make statements that are "considered fraudulent" or violate securities laws.

"Musk cannot now seek to retract the agreement he knowingly and willingly entered by simply bemoaning that he felt like he had to agree to it at the time but now - once the specter of the litigation is a distant memory and his company has become, in his estimation, all but invincible - wishes that he had not."

The judge also rejected Musk's request to quash part of the SEC's demand for documents about his Nov 6, 2021, tweet calling for followers to vote on whether he should sell 10 per cent of his Tesla stock.

The tweet sent the company's share price lower, and the SEC wants to know if it was approved as required. The agency also is investigating possible insider trading after Musk's brother - a Tesla board member - sold US$108 million (S$149 million) in the carmaker's stock a day before the poll.