The Obama administration Friday forced car manufacturer Volkswagen to recall nearly 500,000 cars after it was discovered the German automaker had fitted its vehicles with special technology that can beat environmental tests for reducing smog, according to a new report. The recall, imposed after an investigation by the Environmental Protection Agency, is expected to affect four-cylinder Volkswagen and Audi cars that were manufactured between 2009 and 2015.

The cars' altered emissions control computer, known as a “defeat device,” is designed to switch on when the vehicle is undergoing testing by environmental officials, and turn off when the car is being used normally by its owner. The upshot? The car actually pollutes far more heavily than is reported by Volkswagen, according to the EPA.

“Using a defeat device in cars to evade clean air standards is illegal and a threat to public health,” Cynthia Giles, the EPA’s assistant administrator for the Office of Enforcement and Compliance, told the New York Times. “Working closely with the California Air Resources Board, EPA is committed to making sure that all automakers play by the same rules. EPA will continue to investigate these very serious violations.”

Computer software inside the defeat device is able to hide the cars’ output of the pollutant nitrogen oxide, which the EPA cites as the leading cause of health problems such as asthma and other respiratory issues.

California has also issued a notice of violation to the company on top of the federal government’s complaint.

The allegations against VW will affect 482,000 diesel cars sold in the U.S. since 2009. Among the models recalled are the Volkswagen Passat (model years 2014 and 2015), Volkswagen Jetta (model years 2009-15), Volkswagen Golf (model years 2009–15) and Audi A3 (model years 2009–15).

Analysts speaking with the New York Times said that the notice of violation against VW was meant to send a message that violators of the Clean Air Act will be dealt with harshly by the government.“They want to make it clear that they’re going to crack down on cheaters,” said Frank O’Donnell, president of the environmental advocacy group Clean Air Watch. “They’re cheating not only car buyers but also the breathing public. They want to lay down the law, enforce the law, and show they’re not going to tolerate cheaters. The laws and regulation are only as good as the enforcement.”