Illustration by Alex Castro / The Verge

The US Securities and Exchange Commission is looking into Musk's initial disclosure that he took a substantial stake in the micro-messaging service. In a letter sent last month, the SEC told Musk that he does not appear to have disclosed his acquisition of Twitter shares within the agency's required 10-day window. The agency suggested that Musk used a document that wasn't meant for someone who was hoping to make changes at the company he was buying into.

This is the first public indication that the SEC is looking into Musk's disclosure. The letter, which was filed April 4th but just now made public, requested clarifications from Musk on why he chose to use a form meant for passive investors and whether the agency is wrong about his filing coming in late.

Since the letter was sent, a lot has happened. Musk was offered and accepted a seat on the board, but later decided not to join. The SEC's reading of this initial filing will be affected by all that activity. If there was any uncertainty about Musk's activist intentions as of April 4th, the commission requests clarifications on some of the messages on his account.

Musk has shown little regard for the SEC, which is why this is the latest standoff. Musk tried to escape a settlement he reached with the agency over his funding secured Musk inaccurately claimed he had the money locked down to take the company private The SEC's oversight of Musk's social media activity has been an attempt to chill his exercise of First Amendment rights, according to Musk.