The Securities and Exchange Commission filed an action against Elon Musk dating back to his 2022 acquisition of Twitter, now X. alleging that he was “enriched” to the tune of $150 million by not reporting a stake he had amassed in the social media platform within a required five day window and, instead, buying more stock.

His gain came at the expense of other Twitter shareholders, the Commission said. Had his initial investment been made public in time, the stock would have risen (as it did later) and Musk’s subsequent investment would have cost him more. Likewise, shareholders who sold before Musk disclosed his stake received a lower price.

SEC rules give investors a five-day window to report a 5% or more ownership position in a public company but Musk took longer, “in violation of the beneficial ownership reporting requirements” under the Securities Exchange Act.

According to the SEC’s complaint, Musk saved at least $150 million at the expense of Twitter shareholders by failing to file the beneficial ownership report in a timely manner.

“Congress enacted the beneficial ownership reporting requirements to, among other things, help investors make informed investment decisions by providing information about accumulations of certain classes of equity securities by persons who have the potential to change or influence control of the issuer companies,” the SEC said.

According to the complaint, after Musk failed to “timely file” a beneficial ownership report by   the required date of March 24, 2022, he purchased more than $500 million worth of Twitter common stock between March 25-April 1 2022.

“As alleged, because Musk failed to timely file a beneficial ownership report with the SEC, he was able to make these purchases of Twitter common stock at artificially low prices from the unsuspecting public, who had not yet priced in the undisclosed material information of Musk’s beneficial ownership of more than five percent of Twitter common stock and investment purpose.”

According to the SEC’s complaint, Musk underpaid by at least $150 million for his purchases of Twitter common stock in this period. The complaint further alleges that, due to Musk’s failure to timely file a beneficial ownership report with the SEC, investors who sold Twitter common stock between March 25, 2022 and April 1, 2022 did so at artificially low prices, thereby suffering substantial economic harm.

The SEC’s complaint, filed in the U.S. District Court for the District of Columbia, seeks permanent injunctive relief, “disgorgement of ill-gotten gains” plus prejudgment interest, and civil penalties.