BERLIN — Rising concern over the impact of a potential Russian gas cutoff is fueling the debate in Germany over whether the country should switch off its last three nuclear power plants as planned at the end of this year.

The door to a possible extension appeared to open after the Economy Ministry in mid-July announced a new “stress test” on the security of electricity supplies. It’s supposed to take into account a tougher scenario than a previous test, concluded in May, that found supplies were assured.

Since then, Russia has reduced natural gas supplies through the Nord Stream 1 pipeline to Germany to 20% of capacity amid tensions over the war in Ukraine. It cited technical issues that Germany says are only an excuse for a political power play.

Russia recently has accounted for about a third of Germany’s gas supply, and there are concerns it could turn off the tap altogether.

The main opposition Union bloc has made increasingly frequent demands for an extension of the nuclear plants’ lives. Similar calls are coming from the smallest party in Chancellor Olaf Scholz’s coalition government, the pro-business Free Democrats.

“A lot speaks for not switching off the safe and climate-friendly nuclear power plants, but if necessary using them until 2024,” Finance Minister Christian Lindner, the Free Democrats’ leader, told Sunday’s Bild am Sonntag newspaper.

Lindner called for Economy Minister Robert Habeck, who is responsible for energy, to stop the use of gas to generate electricity.

Calls for extending the use of nuclear power are awkward for the other two governing parties, Scholz’s center-left Social Democrats and, particularly, Habeck’s environmentalist Greens. Opposition to nuclear power is a cornerstone of the Greens’ identity; a Social Democrat-Green government launched Germany’s exit from nuclear power two decades ago.

A government made up of then-Chancellor Angela Merkel’s center-right Union and the Free Democrats set the nuclear exit’s current form in 2011, shortly after the Fukushima nuclear disaster in Japan.

It calls for the three still-operational reactors to go offline at the end of December.

Habeck has long argued that keeping those reactors running would be legally and technically complex and do little to address the problems caused by a shortfall of gas, arguing that natural gas isn’t so much a factor in generating electricity as in fueling industrial processes and providing heating.

“We have a heating problem or an industry problem, but not an electricity problem — at least not generally throughout the country,” he said in early July.

In this year’s first quarter, nuclear plants accounted for 6% of Germany’s electricity generation and gas for 13%.

Lindner said “we must work to ensure that an electricity crisis doesn’t come on top of the gas crisis.”