Photo courtesy of VW.

Photo courtesy of VW.

The U.S. Department of Justice has filed suit against Volkswagen on behalf of the U.S. Environmental Protection Agency over 600,000 vehicles that included software designed to cheat emissions testing for engines that couldn't meet federal Clean Air Act standards.

The federal lawsuit filed Jan. 4 in Detroit also names Audi and Porsche. Discussions between the agency and Volkswagen have appeared to stall over the automaker's plan to recall the vehicles.

"With today’s filing, we take an important step to protect public health by seeking to hold Volkswagen accountable for any unlawful air pollution, setting us on a path to resolution," said Cynthia Giles, the EPA's assistant administrator for enforcement and compliance assurance. "So far, recall discussions with the company have not produced an acceptable way forward. These discussions will continue in parallel with the federal court action."

The so-called defeat software resulted in "thousands of tons of excess" nitrogen oxide emissions in California, according to the California Air Resource Board.

Vehicles named in the lawsuit include both engines affected by the diesel emissions scandal, including the 2.0L and 3.0L engines. The complaint covers about 499,000 2.0L engines and 85,000 3.0L engines since the 1999 model year.

Read the full EPA release here.