The EPA has accused Volkswagen of unlawfully using special software to get around emissions regulations.

Volkswagen allegedly used a "defeat device."

The company allegedly used a so-called "defeat device" on certain diesel models dating back to 2009. The device works by only turning on emissions control when undergoing emissions testing, but not when the car is actually being driven normally and pollution is at its peak. "This results in cars that meet emissions standards in the laboratory or testing station, but during normal operation, emit nitrogen oxides, or NOx, at up to 40 times the standard," the EPA said in a statement.

Using such a device is a violation of the Clean Air Act, which, as The New York Times points out, the EPA has been increasingly cracking down on. In November, the agency hit Hyundai and Kia with a record $100 million fine for violations under the act.

The diesel cars affected by the recall include the 2009 to 2015 Jetta, Beetle, Golf, and Audi A3. The 2014 and 2015 Passat is also included. According to the EPA, that adds up to 482,000 cars, but owners of them aren't being told to take any action just yet.

Correction, September 18th, 2:46ET: This article and its headline originally stated Volkswagen was ordered to recall the nearly 500,000 cars. That is not currently the case.