France faced fresh strikes on Thursday after nuclear power station workers voted to join gathering protests against labour law reforms that have forced the country to dip into strategic fuel reserves due to refinery blockades.
With football fans due to flood into France in two weeks for the Euro 2016 championships, pressure is piling on the government as queues at petrol stations lengthen by the day.
Prime Minister Manuel Valls warned the CGT union leading the disruption at refineries and fuel depots that it "does not make the law in France".
The CGT, locked in an increasingly bitter struggle with the government, has called for its action to be extended today to nuclear power stations that supply 75% of the country's electricity.
The union said late on Wednesday that 16 of France's 19 nuclear stations had voted to join the strike, although CGT official Jean-Luc Daganaud said the effect on power supply would depend on how many workers downed tools.
The union has also called for rallies in major cities, upping the stakes after three months of protests that brought hundreds of thousands on to the streets at their peak at the end of March. The reforms are designed to address France's famously rigid labour market by making it easier to hire and fire workers.
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But opponents say they are too pro-business and will do little to reduce France's jobless rate of around 10%.
France has nearly four months of fuel reserves and President Francois Hollande told a cabinet meeting that "everything will be done to ensure the French people and the economy is supplied".
But with five of France's eight refineries having either halted or slowed production, shortages are becoming acute in many regions and spreading to Paris.
Worried drivers were using online apps to find petrol stations that still had fuel, with many limiting drivers to just 20 litres each.
The Ufip oil industry federation confirmed that with around a third of the country's 12,000 petrol stations running dry, it had begun using strategic reserves.
Ahead of today's possible strike, one nuclear power plant in Nogent-sur-Seine, around 100 kilometres southeast of Paris, is already operating at reduced capacity.