A US financial regulator has sued Elon Musk for allegedly failing to disclose his ownership of Twitter stock and later acquiring shares in the company at “artificially low prices”, stiffing other shareholders.

The Securities and Exchange Commission (SEC) filed suit against Musk late on Tuesday in Washington DC federal court for alleged securities violations. According to the suit, Musk did not disclose that he had acquired a 5% stake in the company in a timely manner, which allowed him “to underpay by at least $150 million for shares he purchased after his financial beneficial ownership report was due”.

Alex Spiro, a lawyer for Musk, told Bloomberg that the SEC’s case amounted to “an admission” that the agency had no case. Musk, Spiro said, “has done nothing wrong and everyone sees this sham for what it is”.

Musk renamed the social network X after purchasing it for $44bn in 2022.