The European Commission is opening an investigation into a leading group of car manufacturers over whether they colluded on clean emissions technologies. The so-called “circle of five” car manufacturers includes BMW, Mercedes Benz, Volkswagen, Audi, and Porsche. “If proven, this collusion may have denied consumers the opportunity to buy less polluting cars, despite the technology being available to the manufacturers,” says Margrethe Vestager, the European Commissioner for Competition.

The EU Commission is concerned that the deployment of emissions limiting technologies may have been hampered by meetings between BMW, Daimler (which owns Mercedes Benz) and the VW Group (owners of Volkswagen, Audi and Porsche). In particular, the development and rollout of “Selective Catalytic Reduction” systems for diesel engines and “Otto Particulate Filters” for petrol engines are thought to have been affected.

The news comes in the wake of a massive emissions scandal that rocked the global diesel car market after it emerged that several companies including Mercedes and Volkswagen installed ‘defeat devices’ that were designed to allow diesel cars to pass emissions tests. Tens of millions of these cars, which produce an illegal and unsafe amount of pollution, are now on the roads. The EU antitrust investigation announced today is not directly related to the investigations into defeat devices.

This collusion may have denied consumers the opportunity to buy less polluting cars

Despite massive fines being levied on guilty car manufacturers, a recent report has suggested that the number of dirty diesels on the roads has continued to grow post-dieselgate. The nitrogen oxides produced by these cars are estimated to cause around 23,500 early deaths in the UK alone, where seven million such vehicles are thought to still be in use. The report estimates a total of 43 million dirty diesels are being driven in Europe.

Last year, a report from Der Spiegel alleged that Volkswagen, Audi, BMW, Porsche, and Daimler formed a secret cartel in the 90s. There, the companies discussed “the technology, costs, suppliers, and even the exhaust gas purification of its diesel vehicles,” according to the German weekly.

Although BMW declined to comment on the investigation, a representative said that it intends to support the work of the EU Commission. It stressed that this current antitrust investigation is distinct from the previous emissions scandal.

Representatives from Daimler and the VW Group were not immediately available for comment, but we’ll update this piece if we hear anything more.