The European Commission has launched legal action against seven nations including the UK for failing to clamp down on emissions cheating exposed by the VW emissions scandal.
Member states have two months to respond.
Officials in Brussels say Germany, Britain, Spain and Luxembourg have failed to impose the same kind of penalties VW faced in the US over its use of illegal emissions cheating software.
Germany and the UK could also be made to account for refusing to share details of breaches of EU emissions laws they discovered through their own investigations earlier this year.
The Czech Republic, Lithuania and Greece are being hauled up for not even including the possibility of fining carmakers over potential violations.
A spokesman for the UK’s Ministry of Transport told Reuters: “The UK will be responding in the strongest possible terms (to the EU action).”
European consumer lobby BEUC praised the action by the EU, however, stating not enough had been done to protect EU citizens.
“It is a strong rebuke of Germany and other countries’ inaction,” said BEUC head Monique Goyens.