The SEC is investigating whether Elon Musk or others committed securities fraud related to his acquisition of Twitter in 2022. A US judge ordered Musk to testify in the SEC's probe, rejecting Musk's arguments that the subpoena amounted to harassment. The SEC is probing Musk's initial buying of Twitter stock before announcing his intention to buy the whole company. Musk has a history of challenging federal regulators like the SEC and NLRB over issues like his tweets and SpaceX employee complaints.