The toll was a cornerstone of the Christian Social Union (CSU) - the Bavarian sister party of Angela Merkel's Christian Social Union (CSU) - election campaign in 2013.
On their insistence, it was written into the coalition agreement with the Social Democrats signed at the end of the same year.
The road charge will be applied to all autobahns and state-run roads and will be paid by foreigners and Germans alike. But Germans will see an equivalent drop in road tax, making the toll de facto a charge against road users from outside Germany.
In an interview with Phoenix, Transport Minister Alexander Dobrindt described the law as “important, urgent and necessary” to raise funds for reinvestment in transport infrastructure.
He added that despite the controversy “the majority of the population are with us.”
“For 12 months the same arguments have come up [against the toll] and no new ones have been produced. We have achieved something in conformity with EU law.”
He stood by an earlier assertion that the law will bring in €500 million per year, saying the numbers were “thoroughly researched.”
Critics have named the toll “the Pegida toll” after the right-wing anti-Islamic protest movement that originated in Dresden last year.
The opposition claims actual income will be closer to €100 million per year.
The Green Party's transport spokesperson said it could be used to repair “perhaps two bridges a year.”
Within the government, support was also thin on the ground.
Social Democrat (SPD) MP Bettina Hegedorn said in the Bundestag, “it'sno secret that the fan block within the SPD in support of the toll is so small that it is invisible.”
But she said the SPD would vote in favour, saying being part of a coalition is about “mutual respect.”
The conservative CSU exist only in Bavaria, and the passing of the law has opened up old tensions between the “free state” and the rest of the country.
Hamburg-based weekly Die Zeit complained bitterly about the country being held hostage by “Bavarian populists” and warned of the damaged caused “Bavarian obstinacy.”
On Monday, last minute changes were made to the bill in an attempt to make it conform to EU law. The price of short term tickets will now be staggered according to the environmental damage caused by each vehicle.
The earlier change making the law apply to Germans was also made with conformity to EU law in mind. But it means that all license plates of Germans will be recorded – a necessary means of proving that Germans have driven on roads where the toll applies.
“The debate over a toll for foreigners has developed into a debate about surveillance of Germans,” complained Die Zeit's Felix Rohrbeck.
The law's critics hope it will fall foul of the Court of Justice of the European Union.
Legal challenges are expected to last several years.