The US Department of Justice (DoJ) has revealed that it is suing Volkwagen after it fitted millions of vehicles with a device to cheat emissions tests.
Following an investigation by US regulators last year, the German can manufacturer admitted using the so-called 'defeat device' to cheat the tests, estimating that around 11 million vehicles were affected.
The emissions scandal has, unsurprisingly, had a knock-on effect on Volkswagen's sales. And it has had to set aside billions of euros to cover expected fines.
The DoJ said it was the first step in "bringing Volkswagen to justice".
The lawsuit filing said: "The complaint alleges that nearly 600,000 diesel engine vehicles had illegal defeat devices installed that impair their emission control systems and cause emissions to exceed EPA's standards, resulting in harmful air pollution."
Cynthia Giles, assistant administrator at the EPA's Office of Enforcement and Compliance Assurance, said: "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.
"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."
Volkswagen is also facing separate criminal charges and is conducting its own internal investigation, which is says will leave 'no stone unturned'.