Under pressure from the European Union to rein in air pollution, the German government said it is considering a plan that would make public transportation free in its most polluted cities, Deutsche Welle reports citing a letter seen by German media.

The letter, sent to European Environment Commissioner Karmenu Vella in Brussels, was written by German Environment Minister Barbara Hendricks, Agriculture Minister Christian Schmidt and chancellery office chief Peter Altmaier.

The German government proposed the free public transportation scheme to encourage people to leave their cars at home, thereby reducing nitrogen dioxide emissions and particulate matter.

They selected five cities to roll out the program: Bonn, Essen, Reutlingen, Mannheim and the town of Herrenberg which is south of Stuttgart — one of Germany's most heavily polluted cities.

The letter also reportedly proposed instating "low emission zones" for large transporter vehicles, increasing the number of electric-powered taxis and boosting incentives for electric cars in general.