Volkswagen is being investigated by the United States Securities and Exchange Commission (SEC) over an April Fools Day marketing stunt in which the company claimed it was changing the name of its U.S. unit to Voltswagen, according to German business magazine Der Spiegel (via Reuters).

The SEC first requested information about the joke name change, which was meant to promote VW's electric cars, in early April, according to the report, which also quoted VW as confirming the investigation.

Automakers often indulge in April Fools Day jokes, but in this case VW claimed it wasn't joking. The Voltswagen name first came to light in a leaked press release that appeared a few days before April 1 and was widely reported on by media. When Motor Authority and other media outlets asked VW public relations directly if the name change was real, a spokesperson indicated it was.

2021 Volkswagen ID.4

2021 Volkswagen ID.4

At least one analyst praised the name change, while VW share prices rose on the day the Voltswagen name was announced, Reuters reported. The fluctuation in stock prices over the fake name is likely what drew the SEC's attention.

VW subsequently confirmed that the announcement, which also included details on changes to vehicle badging, was an elaborate marketing stunt to promote electric cars. The automaker just launched its first mass-market electric car—the ID.4 crossover—and plans to build 28 million EVs by 2028, encompassing 70 different models across the German automaker's many global brands.

This isn't the first time the SEC has investigated an auto-industry prank. In 2018, the agency fined Tesla CEO Elon Musk $40 million after he made misleading statements about taking Tesla private. Musk was also forced to step down as chairman of the automaker.

This also isn't the first VW investigation in recent years. In 2015, the automaker admitted that it used illegal software in diesel engines to cheat on emissions tests, which cost the company billions of dollars.