“We have opened an administrative proceeding (against Porsche AG) at the end of which a court could impose a fine,” a spokesman for the Stuttgart prosecutor's office told AFP, confirming a Bloomberg News report.

Porsche's parent company Volkswagen and fellow high-end subsidiary Audi 
were last year hit with similar “administrative” cases by prosecutors in Brunswick and Munich, which are separate from any ongoing criminal investigations against company individuals.

Both VW and Audi drew a line under their administrative orders by accepting a financial penalty and admitting responsibility for breaching air pollution requirements.

VW paid €1 billion euros while Audi was slapped with an €800 million euro fine.

Under German law, a company can be fined in this way if executives are found to have failed to take the necessary supervisory measures to prevent illegal activities.

In a statement, Porsche said it would fully cooperate with the investigation but reiterated that it believed the company had not fallen foul of its supervisory duties.

The so-called “dieselgate” scandal broke in 2015 when Volkswagen was forced to admit it had equipped some 11 million diesel cars worldwide with software designed to skirt regulatory tests to make the engines seem less polluting than they were.

VW's own-brand vehicles were among those affected by the years-long scam, as well as cars from its Porsche, Audi, Skoda, Seat stable of brands.

The scandal has so far cost the VW group more than €28 billion in penalties, buy-backs and refits, and it remains mired in legal woes at home and abroad.

Prosecutors in Stuttgart have also opened investigations against two 
current and one former Porsche employee, as well as against persons unknown, on suspicion of fraud and false advertising over the dieselgate scandal.