Brussels - The European Commission launched a challenge on Thursday to Germany's planned road toll, which would penalise foreign drivers and so may violate European Union anti-discrimination laws.
The toll, which Germany's parliament approved in March, will make foreign car drivers pay up to €130 a year to use the country's highways.
German drivers would also pay the toll but would receive a corresponding reduction in automobile taxes. Critics say that contravenes EU rules.
"A toll system can only be compliant with European law if it respects the fundamental treaty principle of non-discrimination," European Transport Commissioner Violeta Bulc said in a statement.
"We have serious doubts that this is the case in the final text of the relevant German laws. We are now acting swiftly to clarify these doubts through an infringement procedure in the interest of EU citizens," she continued.
Berlin has two months to respond to Brussels. If the two sides are unable to find an agreement, the case may eventually be settled in court.
The toll is a pet project of German Transport Minister Alexander Dobrindt and his Bavarian Christian Social Union (CSU) party.
The CSU's bigger sister party, Chancellor Angela Merkel's Christian Democrat (CDU), as well as the junior centre-left coalition partner, the Social Democrats (SPD), have been openly sceptical.