Germany’s biggest carmakers were already facing public criticism after an emissions cheating scandal at Volkswagen. Now, they are under formal investigation.

The European Commission opened an inquiry on Tuesday into possible collusion among BMW, Daimler and Volkswagen to prevent the development of clean emissions technology. The investigation adds to a series of problems for the German auto industry, the country’s biggest employer and exporter, which is grappling with the consequences of Volkswagen’s diesel deception, as well as a long-term shift toward electric vehicles and the threat of auto tariffs from the United States.

The announcement by the commission, the European Union’s executive arm, comes nearly a year after officials searched the German automakers’ offices as part of an initial inquiry into possible price fixing. The commission said on Tuesday that it had information indicating that the companies had participated in meetings where they discussed technology to limit harmful emissions. The investigation will try to establish whether the automakers sought to limit the development or rollout of systems to reduce harmful nitrogen oxide emissions from diesel cars or filters to reduce emissions from gasoline engine cars.

“These technologies aim at making passenger cars less damaging to the environment,” Margrethe Vestager, the European Union’s competition commissioner, said in a statement. “If proven, this collusion may have denied consumers the opportunity to buy less-polluting cars, despite the technology being available to the manufacturers.”