Motorists heading to France for the bank holiday are being urged to fill up their tanks at every opportunity as fuel shortages caused by industrial action worsen.
Finding fuel is "extremely difficult" in parts of the country - with long queues forming at pumps with supplies left, the RAC said.
A dispute over labour reforms has led to blockades in towns and cities, and on motorways and bridges, prompting the fuel shortage.
"Try and fill up before you go and be prepared to have to queue," RAC spokesman Simon Peevers said.
Thousands are expected to head across the Channel this weekend despite the risk of being stranded.
Mr Peevers said drivers should fill up before they "need it" but should not cancel their holidays to France.
Fuel shortages were concentrated in northern France but are now affecting the central, western and southern regions of the country, the RAC said.
Drivers are also being urged to stay put if they do not have enough fuel left to get home on one tank.
Simon Williams, for the RAC, said: "Anyone currently in France is going to struggle to find fuel for their return journey and probably shouldn't even attempt to get home unless they can do so on one tank.
"We suspect finding somewhere to fill up in the worst-affected areas will be extremely difficult."
He added: "If you are just about to go to France, you should fill up in the UK before your crossing to give you the best chance of reaching your destination in one go."
The RAC said it was no longer able to help its members find fuel in France and urged motorists to be "mindful" of not running out and getting stranded.
P&O ferries are letting drivers take just five litres of spare fuel on board.
Dan Bridgett, head of communications at P&O, said the ferry company was operating a full schedule but that drivers would only be allowed to carry "up to five litres of spare fuel".
The bank holiday weekend getaway is expected to be the busiest in three years, with more than 15.3 million individual leisure car journeys predicted to take place between Friday and Monday, according to the RAC.
Breakdown recovery firm Green Flag said on Thursday that it was experiencing a 14% rise in the number of its UK customers reporting fuel-related breakdowns in France, and advised drivers to fill up before heading to the continent.
The AA reiterated advice to drivers to refuel regularly while travelling.
Rosie Sanderson, the AA's international travel spokeswoman, said: "The dispute doesn't mean that all fuel stations will find their supplies exhausted, but I'd suggest that drivers keep topping up their tanks when they can rather than risk running out."
She said drivers should not change their plans, but warned against seeking a bargain at pumps across the Channel.
"Fuel is cheaper in France than in the UK and many drivers set off with low fuel and expect to top up when they arrive. But this strategy could backfire, as petrol stations in the Channel ports are running out first.
"We're also urging our members to moderate their driving to get the best fuel economy. The only silver lining might be that there may be less traffic thanks to the dispute, meaning fewer traffic jams, which will allow a car to travel further - typically 300 miles or more - on one tank of fuel."