The US Department of Justice and the Environmental Protection Agency filed a joint lawsuit Monday against Volkswagen for installing illegal "defeat devices" in 600,000 of its diesel engine vehicles. The government accuses the car manufacturer of violating the Clean Air Act by importing and selling vehicles in the US that were designed differently than what Volkswagen described in its EPA certification.

It's the latest headache for the German auto manufacturer since it admitted to illegally installing software in its vehicles to pass federal emissions standards when undergoing lab testing last September. Since then, the scandal has taken its toll on Volkswagen's US sales and prompted the company to issue multiple apologies, as well as launch its own internal investigation into what happened.

But apparently the federal government didn't get the apology. The Justice Department and the EPA are seeking at least $2,750 for each "defeat device," which could total at least $1.65 billion in fines for VW. (A copy of the complaint can be read here.)

In addition to Volkswagen, the complaint also targets two VW-subsidiaries, Porsche and Audi. And in a statement, prosecutors claim that VW's cheat devices "breach the public trust, endanger public health, and disadvantage competitors." And they promise that the lawsuit is only the first step in the government's mission to make VW pay for its alleged crime.

"The alleged misrepresentations allowed almost 600,000 diesel engines to emit excessive air pollution across the country, harming our health and cheating consumers," said US Attorney Barbara L. McQuade for the Eastern District of Michigan, where the lawsuit was filed.

The lawsuit represents the next phase of VW's emission scandal, with some experts predicting that criminal charges could soon follow. A host of private class-action suits from angry Passat and Golf owners could also hit VW in the coming months.

Update: A VW spokesperson responded: "Volkswagen will continue to work cooperatively with the EPA on developing remedies to bring the [diesel] TDI vehicles into full compliance with regulations as soon as possible. In addition, we are working with Kenneth Feinberg to develop an independent, fair and swift process for resolving private consumer claims relating to these issues. We will continue to cooperate with all government agencies investigating these matters."