Consumers should start cutting back on their energy use immediately, the heads of France's three big energy companies said on Sunday.
They issued a warning of social tension throughout winter unless reserves are replenished.
"The effort has to be immediate, collective and massive," Patrick Pouyanne of TotalEnergies, Jean-Bernard Levy of EDF and Catherine MacGregor of ENGIE wrote in a newspaper column in Le Journal du Dimanche.
The call came after the French government said it aimed to return its natural gas reserves to full capacity by autumn.
The energy chiefs wrote that European energy production was further hampered by drought affecting global hydroelectric production.
"The surge in energy prices resulting from these difficulties threatens our social and political fabric and impacts families' purchasing power too severely," they said.
"The best energy is the one we don't use."
They said "every consumer and every company must change their habits and immediately limit their energy consumption, be it of electricity, gas or oil products".
Replenishing reserves of natural gas this summer was a top priority, they said, as is "eliminating the national waste" of energy.
France is less dependent than neighbour Germany on Russian gas as it covers close to 70 per cent of its electricity needs from nuclear energy.
But the International Energy Agency says France needs to accelerate the use of low-carbon technology and energy efficiency solutions if it wants to reach its energy and climate targets.
The IEA said France needs "more sustained and consistent policies" to develop alternatives to fossil fuels, such as wind and solar energy.
On Sunday, the French government announced it could restart a coal-fired power plant in the Lorraine region in north eastern France this winter,
"As a precautionary measure, given the situation in Ukraine, we are reserving the option to reactivate the Saint Avold plant ...if needed this winter," France's energy ministry said in a written statement.
The plans will not affect the phasing out of coal plants in France, the ministry added, noting the operator would offset the emissions through measures like reforestation.
Electricity production from coal will remain below 1%, officials said.