Hulot said on Tuesday it was "unrealistic" to cut nuclear energy’s share of electricity production to 50 percent by 2025, as planned since 2012.
It is currently at 75 percent.
Echoing a warning from grid operator RTE, he added a too speedy reduction meant a danger of power shortages, would increase France’s CO2 emissions and would put jobs at risk.
Gambling on renewables
Some experts argue that this is the best decision for the industrial sector in France.
The 2025 target meant "gambling on the fact that renewable energy is going to develop in a tremendous way over the next 10 to 15 years", according to management union CGE official Alexandre Grillat
"When you look at the last 15 years, we would be justified in questioning whether it will work or not and whether we are not facing the possibility of total electricity outages in France," he told RFI.
The RTE ireport implies that closing plants hastily would make it necessary to replace nuclear power with gas or continue using coal-fired plants, Grillat says, adn that would mean emitting more CO2.
He also argues that estimates of future electricity demand have been biased and unrealistic.
Pushed back five to 10 years
Hulot said the target of 50 percent nuclear will be pushed back to 2030 or even 2035.
So what difference would that decade make?
"It actually doesn't make that much of a difference from a technical point of view," according to Yves Marignac, a nuclear expert at energy consultants Wise-Paris.
"We think that more renewables and more energy efficiency could still allow to meet the 2025 objective. What it does though is relax the constraints from a political point of view."
Marignac says that could undermine the politicians' sense of urgency.
"And, if France does not accelerate on efficiency and renewables, then it will find itself again, in a few years' time, with the conclusion that its objectives could not be met. So there is a real political risk in differing the objective, we would rather expect accelarating on action."
Alix Mazounie, an energy campaigner at Greenpeace France, says even five years will make a huge difference.
"Our nuclear reactors are currently nearly all 40-years-old, which is the deadline that was initially set for them to shut down," Mazounie told RFI.
"Now, if we don't make a decision in the next couple of years on which reactors we plan to shut down and we decide that, basically, they will stay on, if we don't unplug them quickly, they will become more and more unsafe, they will cost more and more money to the French state, because the maintenance of our nuclear reactors is already extremely costly."
The older the reactors get, the more expensive it becomes to maintain them and make sure that they are safe and operational, she pointed out.
Renewables and jobs
Mazounie also argues that postponing the deadline could prevent the renewable energy sector from developing properly.
"It impacts the renewable energy sector drastically. Why? Because the fact that we have a lot of nuclear electricity in our system means that there is currently very little space for renewable energy."
France is at present able to meet its electricity needs.
"So there is just no space for both nuclear energy and renewable energy," Mazounie argues. "So if we want to develop renewable energy, we must make space for it by shutting down nuclear reactors as quickly as possible."
Grillat the trade unionist is anxious about jobs.
Energy policy must create long-term employment in France, he argues, and renewables will mean more imports, often from China.
"You're on, let's talk about it" he said. "But show all your cards to the table so we can have a prpoer reality check when it comes to the industry."
Hulot, a former high-proifile environmental campaigner, said President Emmanuel Macron's government remains committed to reducing nuclear energy and ordered his ministry to produce a new timetable.