European antitrust authorities plan to fine Daimler, BMW and VW up to EUR1bn each for colluding on reducing the effectiveness of exhaust filtering systems, Reuters reported, citing German weekly Der Spiegel.

Der Spiegel reportedly said the carmakers collaborated to reduce the size of Adblue tanks which help to reduce harmful nitrogen oxide emissions [as part of selective catalyst reduction diesel exhaust emission equipment] and agreed not to include filters on petrol engine vehicles to reduce fine particulate matter.

BMW declined to comment to Reuters. Daimler said it was cooperating with the European authorities and had applied for the status of a cooperating witness in the proceedings. Volkswagen said it was cooperating with authorities.

Reuters noted such strategic cooperation among German carmakers is not unusual but companies found guilty of breaching EU cartel rules face fines of as much as 10% of their global revenues.

The European Commission also declined to comment to the news agency.