Billionaire Elon Musk has doubled-down on his long running spat with the SEC, accusing regulators of attempting to stifle his First Amendment rights.

Updated at 9:39 am EST

Tesla  (TSLA) – Get Tesla Inc Report CEO Elon Musk accused the U.S. Securities and Exchange Commission of targeting both him and the clean-energy carmaker in an ‘unrelenting’ investigation aimed at limiting his right to free speech.

Tesla attorney Alex Spiro, who is also representing Musk, told U.S. District Judge Alison Nathan that the SEC’s probe into Tesla — which began in 2018 — is motivated by the billionaire’s vocal criticism of U.S. government policy.

Earlier this month, Tesla said it received an SEC subpoena related to a 2018 agreement between the agency and the carmaker to limit Musk’s Tweets on material information related to the world’s most valuable carmaker. 

Tesla, however, received the subpoena on November 16 of last year, just says after Musk asked his 68 million Twitter followers if he should sell 10% of his stake in the company, a move that triggered a 12% slump in Tesla stock.

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“Enough is enough,” Spiro wrote in a letter to the Manhattan district court. “The SEC seems to be targeting Mr. Musk and Tesla for unrelenting investigation largely because Mr. Musk remains an outspoken critic of the government; the SEC’s outsized efforts seem calculated to chill his exercise of First Amendment rights.” 

“The SEC’s outsized efforts seem calculated to chill his exercise of First Amendment rights rather than to enforce generally applicable laws in evenhanded fashion,” the letter added.

Tesla shares were marked 1% lower in early Thursday trading to change hands at $915.00 each. The stock is down around 21.3% from when Musk first Tweeted his indications to sell a 10% stake in early November.

Musk agreed to settle fraud charges with the SEC in October of 2018 in a deal that allowed him to remain CEO of the company he co-founded, but forced his resignation as chairman of the board.

The SEC said Musk had made false and misleading” statements on August 7, 2018 when he told his Twitter followers that he had “funding secured” to take the Tesla private at a price of $420 per share. 

Musk agreed to pay $20 million — while Tesla agreed to pay the same amount — to the SEC in exchange for Musk’s departure from the board and the naming of two new independent directors and a chairman.