Gensler, Musk and Spiro did not respond to requests for comment on Thursday.
Musk's lawyer argued in his letter that the SEC has engaged in "more than six years of harassment" of Musk via investigative activity, including by reopening an investigation into the billionaire's health tech venture Neuralink this week.
Spiro also wrote that he had personally been subpoenaed by SEC staff but refused to comply. He accused the agency of an "improperly motivated campaign against Mr. Musk and the individuals and companies associated with him," and demanded to know whether the White House or the SEC had directed this action against his client.