France's prime minister warned striking oil industry workers Sunday that the government might once again use its requisition powers to force workers back to their posts to ease fuel shortages.
Left-wing leader Jean-Luc Melenchon meanwhile backed calls by some trade unions for a general strike on Tuesday.
Elisabeth Borne told TF1 television that if the situation remained tense Monday, then the authorities would proceed with more requisitions like the ones enforced last week.
About 30% of service stations were experiencing supply problems for one type of fuel or another, she said. "That's too many."
She appealed to those TotalEnergeies workers still on strike not to "block the country with all the difficulties that that creates".
After three weeks of industrial action, three out of seven of the country's oil refineries and five major fuel depots (of around 200) are affected, the government said.
Geoffroy Roux de Bezieux, president of the Medef business lobby group, told Radio J that another week of fuel shortages might have a real impact on the economy.
"This isn't a normal strike," he added. "The right to strike has limits."
Farmers are struggling to find the fuel they need to plant their winter crops on time, particularly in the north of the country.
'General strike'
Borne's warning came after tens of thousands marched through Paris Sunday to protest the rising cost of living, and government inaction over climate change.
The demonstration was called by the left-wing political opposition and led by Melenchon, head of the France Unbowed (LFI) party.
While most of the march passed peacefully, security forces did fire teargas and launched baton charges on several occasions after being pelted with objects. On the fringes of the march, masked men dressed in black ransacked a bank.
Some protesters wore yellow florescent vests, the symbol of the often violent anti-government protests in 2018 that shook the pro-business government of President Emmanuel Macron.
"The people at the top are out of touch," said Christopher Savidan, an LFI activist out of work for five years.
"We pay taxes – we don't know why. Everything is going down the drain."
Opponents of Macron are hoping to build on the momentum created by the refineries dispute, which began at the end of September.
"We're going to have a week the likes of which we don't see very often," Melenchon told the crowd.
"Everything is coming together. We are starting it with this march, which is an immense success."
Melenchon also called for a "general strike" Tuesday. Some but not all unions have already declared the date a national day of strikes targetting road transport, trains and the public sector.
Huge profits
The huge profits made by energy groups due to record fuel prices have led to some sympathy for employees pushing for higher wages.
But some drivers struggling to find fuel for their vehicles are losing patience. Many companies have cut back on travel and deliveries, and even emergency service vehicles face shortages.
A poll by the BVA polling group released Friday suggested that only 37% of people supported the stoppages.
The strikes and protests are being closely watched by the government, which is aiming to pass a highly controversial change to the pensions system in the next few months.
Macron, who won re-election in April, has pledged to push back the retirement age from 62, with the reform scheduled before the end of the winter.
"I'm really worried," one ruling party MP told AFP last week on condition of anonymity. "We need to find a route between the need for reforms and the fact that people are riled up and tired."
TotalEnergies announced on Friday that it had reached a pay deal with the two largest unions representing staff at its refineries, raising hopes of an end to the standoff.
But the hardline CGT union has refused to accept it, with its members continuing to maintain picket lines.