The conservatives of chancellor-in-waiting Angela Merkel and the Social Democrats (SPD) are in talks to forge a power-sharing alliance that should be in place by the end of November.
The former election rivals have made steady progress on a series of issues, from budgetary policy to renewable energy, but the future of atomic power seems set to be a key battlefield in the coming weeks.
"The lifetime of nuclear power stations cannot be extended," SPD chairman Franz Muentefering told Bild am Sonntag newspaper in an interview to be published on Sunday.
The SPD and their former government partners, the Greens, pushed through a law in 2000 to phase out Germany’s 17 atomic energy plants by 2020.
However, the conservatives are keen to provide Germany, a large importer of oil and gas, greater energy security and allow industry to earn more by extending the life of their plants.
The conservative premier of Baden-Wuerttemberg, Guenther Oettinger, said in a guest commentary in Bild am Sonntag that energy firms would then have more time to boost renewables.
"At least in the next four years, no secure and economic nuclear power station should be taken off the network," he said, while acknowledging that nuclear-free energy was something to wish for.
SPD environment expert Hermann Scheer told Handelsblatt his party could not vote for any extension, arguing energy firms would simply seek further extensions later.
Working group talks are to resume next week.
Nuclear power, which became extremely unpopular in Europe after the 1986 Chernobyl accident, has been making a comeback. The first new nuclear plant on the continent in years is being built in Finland.
One of the reasons for its return to favour is the fact that nuclear reactors emit virtually no greenhouse gases.