The United States Securities and Exchange Commission (SEC) is investigating Volkswagen’s “Voltswagen” debacle to see how the stunt affected the automaker’s stock price, and whether it broke any securities laws, according to Der Spiegel.

The faux rebranding took place on March 29th, when Volkswagen’s American subsidiary “accidentally” published a draft press release about changing its name to Voltswagen in a nod to the larger company’s push into electric vehicles.

After some news outlets reported on that apparently errant admission, the company followed up with an official press release on March 30th, which included quotes from Volkswagen of America CEO Scott Keogh claiming the change was really happening.

Ultimately, the stunt turned out to be a poorly telegraphed (and early) April Fools’ joke, and multiple news outlets — including the Associated Press — said that Volkswagen of America representatives lied and told them the name change was really happening.

Volkswagen’s stock price increased as much as 12.5 percent at one point, the equivalent of billions of dollars of market value. It’s unclear what the SEC is specifically interested in learning about, or what laws VW could have even broken in the first place. But the agency has previously come after Tesla CEO Elon Musk for tweeting things that turned out not to be true about his company, and Volkswagen has a well-documented history of lying to regulators in the US, too.