It has sent their governments formal requests to reform their systems, which, if ignored, could lead to a referral to the European Court of Justice (ECJ).
The Dutch government is being pushed to lift its imposition of registration taxes on cars leased and registered abroad, that Netherlands residents want to use in their own country.
The Greeks are being pressed over rules allowing registration taxes to be higher for imported cars than those first registered in Greece.
Brussels is criticising Poland for charging higher excise duty on imported second-hand cars than on originally Polish-registered cars.
Meanwhile, the commission is formally threatening legal action at the ECJ against Denmark, Luxembourg, Portugal, Cyprus and the Czech Republic for failing to write into their national laws, an EU directive harmonising all member states’ registration certificates. Brussels says the law will help: police check whether drivers are authorised to use a vehicle; foreign officials understand such documents; and the speeding of formalities approving the use of vehicles previously registered in other EU countries.