E.ON (>> E.ON SE), RWE (>> RWE AG) and EnBW (>> Enbw Energie Baden Wuerttemberg AG) have demanded exemption from the tax, introduced in 2011, and are claiming back the roughly 5.8 billion euros ($6.2 billion) they have already paid.

The tax requires companies to pay 145 euros per gram of nuclear fuel each time they exchange a fuel rod, usually about twice a year. The utilities say they only agreed to pay this in return for being granted longer lifespans for their plants as was promised in a pre-Fukushima agreement.

The European Court of Justice last year ruled the tax did not breach European Union laws, but utilities are pinning their hopes on the German Constitutional Court, which theoretically could still rule the tax illegal.

In a separate case, the court had ruled this week that a 2011 decision to shut down all existing nuclear plants by 2022 at the latest violated some property rights, paving a way to claim back stranded investments and power production rights.

($1 = 0.9294 euros)

(Reporting by Tom Kaeckenhoff; Writing by Christoph Steitz; Editing by Ruth Pitchford)

Stocks treated in this article : Enbw Energie Baden Wuerttemberg AG, RWE AG, E.ON SE