Germany’s three largest carmakers secretly agreed to equip their vehicles with inferior emissions equipment, European authorities said Friday, a finding that could expose Volkswagen, Daimler and BMW to a large share of the blame for poor air quality in Europe that is believed to cause thousands of deaths annually.

The preliminary decision by the European Commission escalates a scandal that began in 2015 when Volkswagen confessed that it had equipped millions of vehicles in Europe and the United States with software designed to dupe emissions testers. If the finding published Friday is confirmed, the carmakers could face billions of euros in fines.

The latest accusation against the carmakers is, in many ways, even broader than Volkswagen’s cheating. The commission said that for most of a decade, Volkswagen, Daimler and BMW had agreed not to compete on key components of their pollution controls, violating antitrust laws and contributing to bad air quality in traffic-clogged cities like London and Paris.

Instead, the carmakers colluded to restrict the size of tanks used to hold a fluid that cleanses diesel emissions, the commission said, while delaying deployment of filters that remove cancer-causing particles from the exhaust of gasoline engines.