Musk has had a contentious relationship with the SEC, and last year, four lawmakers urged the commission to investigate whether he misled investors regarding the safety of Neuralink's brain implant, potentially constituting securities fraud.
It remains uncertain how effective the SEC's actions against Musk might be.
The billionaire, who also leads Tesla and SpaceX, is poised to gain significant influence after investing over a quarter of a billion dollars to support Donald Trump's campaign in the upcoming presidential election. His businesses are likely to remain largely shielded from regulatory scrutiny.
Furthermore, President Trump appointed Mr. Musk to a task force dedicated to implementing comprehensive reforms within the U.S. government.
In the correspondence, Mr. Spiro stated unequivocally that neither he nor Mr. Musk would be intimidated by the SEC, and asserted their commitment to safeguarding their legal rights.
The SEC and Neuralink did not offer immediate responses outside of standard business hours.
A federal judge dismissed the SEC's motion for sanctions against Mr. Musk in November due to his failure to comply with a court order to provide testimony related to the investigation into the Twitter acquisition. This investigation focused on potential securities law violations in 2022.
The SEC previously initiated legal action against Mr. Musk in 2018 concerning his tweets about privatizing Tesla. This matter concluded with a settlement wherein Mr. Musk paid a $20 million penalty, agreed to a pre-approval process for specified tweets managed by Tesla's legal team, and stepped down as chairman.