Over the past few weeks, Mr. Musk had taunted the S.E.C. in posts on X about the potential for filing a lawsuit. In December, he shared a letter that his lawyer, Alex Spiro, had sent to the agency, rejecting a settlement offer in the case.
On Tuesday, Mr. Spiro denounced the regulator’s latest filing.
“Today’s action is an admission by the S.E.C. that they cannot bring an actual case, because Mr. Musk has done nothing wrong and everyone sees this sham for what it is,” Mr. Spiro said in a statement. The agency had waged a “multiyear campaign of harassment” against Mr. Musk but filed “a single-count ticky-tack complaint,” Mr. Spiro added.