The Greens, minority partners in France's Socialist-led administration, lashed out at Industrial Recovery Minister Arnaud Montebourg for comments in which he lauded France's nuclear industry as a "tremendous asset."
"We need energy that is not too expensive," Montebourg said.
France is the world's most nuclear-dependent country, operates 58 reactors and has been a leading international proponent of atomic energy.
But in a deal with the Greens before this year's parliamentary and presidential elections, the Socialists promised to reduce reliance on nuclear energy from more than 75 percent to 50 percent by shutting 24 reactors by 2025.
The Greens, who have 17 seats in the 577-member National Assembly and two ministers in the government, have pushed for alternative sources like wind and solar power to replace nuclear energy.
"This is a provocation.... It is very worrying to see these statements from someone who is not isolated, who is an important member of the government," said former Green presidential candidate Noel Mamere.
"If there is no explanation or questioning of Mr. Montebourg's statements, we environmentalists will be entitled to question the validity of the agreements that saw us enter this majority," he said.
The vice president of the Greens' parliamentary group, Denis Baupin, said Montebourg's remarks were "completely at odds with reality", while a Green Party spokesman said they were "isolated statements" that did not represent government policy.
Montebourg said Monday he had been "talking sense", and following Hollande's election promises. He noted that the nuclear industry employed more than half a million people directly or indisrectly in France.
Interior Minister Manuel Valls backed his colleague, saying nuclear energy was "undeniably" a part of France's energy future.
"We need nuclear (energy), even if we are reducing its share in the decade to come," Valls said.
Green Party Housing Minister Cécile Duflot downplayed the remarks, saying President François Hollande's government would stick by its promises.
"This agreement will be met. The president's commitments apply to everyone," Duflot said.
"I am among those who believe that what commits a government are its actions," she said.
Socialist Party spokesman David Assouline also said the remarks were an expression of Montebourg's "personal feelings" and did not reflect government policy.
Environmental group Greenpeace denounced the "cacophony" of different opinions within the government on nuclear policy.
"This situation is, unfortunately, typical of the methods Hollande began using during the presidential campaign: considering everyone's opinion without making any clear or strategic choice," Karine Gavand, head of political affairs at Greenpeace, said in a statement.
France's reliance on nuclear power has been increasingly called into question since the Fukushima disaster in Japan, which prompted Germany to announce plans to shut all of its reactors by the end of 2022.