European Union antitrust regulators have charged BMW, Daimler and Volkswagen with colluding to block the rollout of emissions cleaning technology in a move that could lead to hefty fines.
In the latest emissions scandal to hit the auto industry, the European Commission said it had sent so-called statements of objections to the companies setting out the charges, nearly two years after carrying out dawn raids at their premises.
It said the collusion occurred between 2006 to 2014 and took place during the carmakers' technical meetings.
"Daimler, VW and BMW may have broken EU competition rules. As a result, European consumers may have been denied the opportunity to buy cars with the best available technology," European Competition Commissioner Margrethe Vestager said in a statement.
The EU focus is on selective catalytic reduction systems to reduce harmful nitrogen oxides emissions of diesel passenger cars through the injection of urea, which is also called AdBlue, in the exhaust gas stream.
It is also concerned about potential collusion on "Otto" particle filters to reduce harmful particle emissions from exhaust gases of petrol passenger cars.
A Volkswagen spokesman confirmed that the German automaker had received the report and would "examine the complaints and issue a statement after evaluating the investigation file as part of its co-operation".
BMW also said it would examine the "statement of objections", adding that it "regards these proceedings as an attempt to equate permissible coordination of industry positions regarding the regulatory framework with unlawful cartel agreements".
A spokeswoman from Daimler, which makes Mercedes-Benz cars, meanwhile said the firm was aware of the report but had already been co-operating with investigators and "does not expect to receive a fine in this matter".
EU fines could go as high as 10% of a company's global turnover.