German Chancellor Angela Merkel's governing coalition has been put on notice that it will face a fight over any change to the law on nuclear energy without approval from the country's upper house of parliament.

Green Party leader Claudia Roth threatened on Sunday to press for a judicial review at the Germany's Constitutional Court if the government moved to extend the operational lifetimes of nuclear power plants without consent from the Bundesrat.

Speaking to public broadcaster ARD, Roth said that a number of Germany's state governments were unhappy about a proposed delay to the closure dates.

Green Party leader Roth says several states oppose a change

The deputy premier of the state of North Rhine-Westphalia, Sylvia Loehrmann, also said that the government could expect what she described as "bitter resistance" from that state's coalition, which is made up of the SPD and her Green Party.

"We will exhaust every legal possibility, right up to the Constitutional Court," the Green party's Loehrmann told the Tagesspiegel newspaper on Sunday.

According to a law passed in 2002 by the then-ruling SPD and the Green coalition, all of Germany's nuclear power plants are to go off line by 2022.

Chancellor Merkel's government has said that it intends to extend the deadline by a period that has yet to be determined. Until recently, it had been thought that any legal change would need to be approved by the Bundesrat, Germany's upper house, which represents country's 16 states.

The Constitutional Court may ultimately decide the matter

However, after the May election in North Rhine-Westphalia, the center-right coalition lost its majority in the upper chamber.

Soon afterward, Merkel's chief of staff, Ronald Pofalla, announced possible plans to bypass the Bundesrat entirely - infuriating opposition parties.

Whether or not the government needs the agreement of the Bundesrat is not clear.

Dissent within coalition

Opinion within Merkel's CDU is also divided.

The CDU premier of the state of Saarland, Peter Mueller, has questioned the need for an extension.

Environment Minister Norbert Roettgen is seeking a consensus

"We need an energy supply that is safe, sustainable and affordable," Mueller said in Sunday's edition of the Bild am Sonntag newspaper.

"I believe that we would be able to achieve that without the extension of the lifetimes of nuclear power plants."

Environment Minister Norbert Roettgen of the CDU's Bavarian sister party, the Christian Social Union, argued for a new limited nuclear plant extension in the Monday edition of Bremen's Weser Kurier, stressing that nuclear power was only needed until alternatives could be found.

"It is a very rational approach, which is linked with enormous economic opportunities for Germany. People in Germany understand that, better apparently than so many critics."

In the same newspaper's online edition on Sunday, Baden Wuertemberg's CDU premier, Stephan Mappus, who wants to see the final shut down date extended by 15 years, criticized Roettgen for not adopting a clearer line in favor of an extension.

Richard Connor (AP/dpa/AFP/Reuters)

Editor: Chuck Penfold