San Francisco, Feb 18 (IANS): Tesla and SpaceX CEO Elon Musk has slammed the US Securities and Exchange Commission (SEC), saying the agency is targeting him and stifling his free speech.

Musk's attorneys made the allegations in a letter to Judge Alison Nathan, who oversaw the 2018 settlement with the SEC over a controversial tweet by Musk that said he had funding secured to take Tesla private, reports The Verge.

"Worst of all, the SEC seems to be targeting Mr. Musk and Tesla for unrelenting investigation largely because Mr. Musk remains an outspoken critic of the government," read the letter.

"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."

Musk and Tesla wrote to the Southern District of New York court accusing the SEC of conducting a "harassment campaign."

The regulator allegedly broke a promise to pay Tesla shareholders $40 million as part of its 2018 settlement with Musk over his controversial tweet.

Musk was charged with making false and misleading statements, ordered to pay a $20 million fine and required to step down as Tesla chairman for three years.

According to the SEC's complaint against him, Musk tweeted on August 7, 2018 that he could take Tesla private at $420 per share -- a substantial premium to its trading price at the time -- that funding for the transaction had been secured, and that the only remaining uncertainty was a shareholder vote.

The SEC's complaint alleged that, in truth, Musk knew that the potential transaction was uncertain and subject to numerous contingencies.

Musk's misleading tweets caused Tesla's stock price to jump by over six per cent on August 7, 2018 and led to significant market disruption.