Tesla founder Elon Musk speaks at the unveiling event by "The Boring Company" for the test tunnel of a proposed underground transportation network across Los Angeles County, in Hawthorne, California, December 18, 2018.

The lawyers of Tesla CEO Elon Musk shot back at regulators on Monday night, arguing that the Securities and Exchange Commission was broadly overreaching and infringing on Musk's First Amendment rights by seeking to hold him in contempt of court.

Musk had until Monday to explain why he shouldn't be held him in contempt of court over a tweet on Feb. 19, published outside trading hours, which the SEC said violated a September settlement agreement with the unpredictable CEO.

His lawyers disagreed, arguing that the tweets in question complied with the earlier SEC settlement terms. They said the CEO "has dramatically reduced his volume of tweets generally and regarding Tesla in particular," and has been diligent — even self-censoring — in his efforts to comply with the terms of that earlier settlement.

Last September, the SEC sued Musk for a separate tweet on Aug. 7 in which he said Tesla had secured funding needed to take the electric car maker private at $420 a share. That claim wasn't true, and sent Tesla's stock soaring initially. Musk later had to walk back the claims.

After that, and as part of a settlement agreement between them, Musk personally paid a $20 million fine. He also agreed to step down as Tesla chairman and to have an appointed in-house attorney vet his tweets, or any other public statements that could affect Tesla's stock price.

In the recent tweet on Feb. 19 that inspired the contempt proceedings, Musk said, "Tesla made 0 cars in 2011, but will make around 500k in 2019." The SEC said that tweet was not approved according to the terms of the earlier settlement, and was inaccurate.

Musk's frequent and sometimes controversial use of Twitter has raised concerns among investors about his fitness to serve as an officer of a public company. Some former SEC attorneys say the agency could suspend him from serving as Tesla CEO.