The European Union has opened a legal case against Germany over Berlin's plan for a highway car toll to raise money from foreign drivers.

EU transport Commissioner Violeta Bulc said Thursday the infringement case was opened because she had "serious doubts" the toll would be in line with EU non-discrimination laws, since German car owners would be compensated by an equivalent cut in a separate car tax.

The plan calls for the system to start in 2016. Germany's transport minister has said it will raise 500 million euros ($550 million) annually.

Germany now has two months to reply to the EU's legal questions on the case.