Officials have taken the extraordinary step of warning some flights landing at France's main airport to come with enough fuel to get back home, bracing for a possible fuel shortage after a new round of protests Saturday against plans to raise the retirement age to 62.

Police estimated some 825,000 people marched in cities across France to protest President Nicolas Sarkozy's plan to extend the retirement age to keep pension coffers full. That is fewer than during an Oct. 12 march _ and far lower than the union estimate of 3 million. But unions are not relenting in fighting for what the French see as a near-sacred right to retire at 60.

A sixth round of nationwide protests is scheduled for Tuesday, a day before the Senate votes on the retirement reform, which must still return to both houses due to amendments tacked on during debates.

"I think the French understand that those who are blocking the country are at the head of the government," Francois Chereque, head of the moderate CFDT union, said on BFM-TV. He later called on the government to "suspend the parliamentary debate."

Schools, trains, public transport and even garbage collection in Marseille have been blocked by intermittant strikes to pressure Sarkozy to back down. The possibility of a long-term fuel shortage appears to be the most worrisome outcome of the protest movement.

All 12 of France's fuel-producing refineries have been hit by strikes that started Tuesday and numerous fuel depots are blocked, triggering a run on gas pumps by fearful motorists. In an extraordinary move, police were called in Friday to force three crucial fuel depots to reopen.

Finance Minister Christine Legarde tried to assuage fears, insisting Saturday that there was no shortage of gasoline.

"Today, there is no reason, no reason, I repeat, to panic because there is no risk of shortages," she told BFM-TV on Saturday, noting that only 230 of the country's 13,000 gas stations were out of fuel. "There are weeks of reserve."

The same could not be said for Charles de Gaulle airport, north of Paris, which moved into a Plan B mode to keep planes flying in and out of the European hub while conserving a limited fuel supply.

The Civil Aviation authority sent out an advisory Friday night to airlines making short- and medium-haul flights to Paris' Charles de Gaulle airport to arrive with enough fuel to get home, spokesman Eric Heraud said Saturday.

"They must come with a maximum capacity in their fuel tanks," Heraud told The Associated Press by telephone. "Obviously, these instructions apply only to short- and medium-haul flights" of no more than four to five hours because trans-Atlantic flights cannot "double carry" fuel, he said.

The pipeline from the Atlantic port city of Le Havre that feeds fuel to Charles de Gaulle airport and the smaller Orly, south of Paris, has been working only intermittently. A fresh flow Saturday extends fuel reserves at Charles de Gaulle until Wednesday, said Heraud.

"That leaves time for parallel supply means" notably by truck, he said, adding that the four-day grace period was considered good.

Orly airport has 17 days' worth of available fuel, Heraud said.

Earlier, the Ecology Ministry had said fuel stocks were good only until Tuesday.

"I don't say we can't guarantee beyond Tuesday ... we will find other solutions," a ministry spokesman said by phone. He said France had not yet resorted to emergency fuel imports from neighboring Italy or Spain. He could not be identified by name in keeping with ministry policy.

A sign Saturday at a gas station in Feyzin, near the southeastern city of Lyon, announced a diesel fuel shortage at all pumps, frustrating motorists there and elsewhere.

"When the government says there will be no shortage, it means there will be a shortage," said Bernard Martin, a 60-year-old retiree who found no fuel at a Carrefour gas station in Ecully, near Lyon. "Since this morning, there is no more diesel fuel."

Dominique Bussereau, France's transport minister, authorized oil companies to use some reserves after trucking companies complained of difficulties finding fuel.

Countries across Europe are cutting spending and raising taxes to bring down deficits and debts that hit record levels after the 2008 financial crisis resulted in the worst recession in 70 years. Labor leaders, students and civil servants are fighting back.

"(These protests are) an attempt to say stop abusing the workers and citizens," Christian Coste, head of the CGT Union at Total's La Mede refinery, told Associated Press Television News on Saturday. "We are not here to bring France to its knees and create a shortage, we are here to make ourselves heard."

Also Saturday, hundreds of thousands of Italian metal workers and other union members marched past the Colosseum in Rome to demand protection for workers as Italy tries to deal with its own economic woes.

Workers have been striking for five days straight at the La Mede refinery in southern France.

The Mediterranean port city of Marseille, where some docks were shut down, grappled with problems that above all perturbed pedestrians: garbage. Uncollected for a fourth day, the stench rose as piles of rubble mounted in the streets. Some people set the messes afire, but firefighters moved in to extinguish the flames.

Sarkozy's pension reforms _ especially raising the retirement age from 60 to 62 _ are seen by unions as a betrayal of a basic right. The government has refused to budge on the central issue, and Labor Minister Eric Woerth reiterated Saturday that the government won't change its mind.

Even at 62, France would have one of the lowest retirement ages in Europe.

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Associated Press Television News in Paris and writer Jean-Marie Godard in Paris contributed to this report.