FRANKFURT E.ON AG, Germany's largest utility, is seeking 8 billion euros ($10 billion) of compensation in a potential industry-wide claim against the government following its decision last year to shut down nuclear power stations.
Earlier on Wednesday, the Frankfurter Allgemeine Zeitung newspaper reported that German utilities including E.ON were seeking a total of 15 billion euros in damages over the government's move.
Germany's constitutional court plans to ask this week for the views of the government and other stakeholders about the validity of the claims, the paper said.
In a decision sparked by the disaster at Japan's Fukushima reactor, Germany closed eight reactors last summer and accelerated the closure schedule for the remaining reactors, which must shut by 2022.
A spokesman for E.ON said the firm was optimistic the case for compensation would be successful.
A spokeswoman for rival RWE declined to comment on the sums involved while the case was being examined by the court. RWE has already said the negative impact on its earnings from the decision to exit nuclear power amounted to around one billion euros.
E.ON has always stressed it is not against the government's greater focus on renewable energy over nuclear power and fossil-fuels, but believes its property rights have been infringed.
Nuclear operators are also arguing with the government about its plans to continue gathering a new fuel rod tax for production volumes they had counted on producing, but which have now been lost.
They have incurred losses as well because they had to buy some power from the market to meet delivery commitments they could no longer fulfill once the nuclear plants were shut, and stand to face higher decommissioning costs than anticipated.
Germany's other two nuclear operators, Vattenfall Europe, the German arm of the Swedish utility group, and EnBW said they had not yet decided whether to bring a complaint.
"We are preparing a decision but it is open what it will be. The term for a complaint to be lodged ends in early August," said a spokesman for EnBW in the Baden Wuerttemberg state.
A Vattenfall spokeswoman also said a decision would be taken in due course.
E.ON and RWE shares gained 2.2 percent and 1.7 percent respectively on the news.
($1 = 0.8028 euros)
(Reporting by Matthias Inverardi, Vera Eckert and Hendrik Sackmann; Editing by Mark Potter)