PARIS - French oil workers defied the government's demand Monday to get back to work and end fuel shortages, stepping up the fight against President Nicolas Sarkozy's retirement reforms. Youths and truckers joined in, facing off against riot police and creating chaos on the roads.

Strikers have blockaded a dozen French refineries and numerous oil depots in the last week as part of widespread protests over Sarkozy's plan to raise the retirement age to 62, a reform the French Senate is voting on Wednesday.

Workers are angry because they consider retiring at 60 a pillar of France's hard-won social contract -- and fear this is just the first step in eroding their often-envied quality of life. Critics say Sarkozy wants to adopt an "American-style capitalist" system and claim the government could find pension savings elsewhere, such as by raising contributions from employers.

Sarkozy's conservative government points out that 62 is among the lowest retirement ages in Europe, the French are living much longer and the pension system is losing money already.

The strike by oil workers has been the most disruptive tactic yet -- and in response, the Interior Ministry opened a crisis coordination center Monday just to focus on the conflict.

Fearful motorists have flocked to gas stations in panic and found many empty, while aviation authorities have been forced to tell short-haul planes coming in to make sure to bring enough fuel to get back.

The government ordered airlines to drastically cut back their flights into France on Tuesday, when labor unions plan new nationwide protests and strikes across the public sector. Severe disruptions to air travel, public transport, schools and other facilities are expected.

Striking oil workers piled up tires and set them ablaze Monday in front of a refinery at Grandpuits, east of Paris, after authorities issued a legal order insisting that some reopen the facility. Workers said they would refuse, as curls of heavy black smoke wafted into the air.

Other employees and residents formed a "human chain" to prevent people from entering the plant.

Dozens of oil tankers remained stuck in the Mediterranean, anchored outside Marseille's two oil ports, where workers have been on strike for more than three weeks to protest a planned port reform as well as the retirement changes.

Prime Minister Francois Fillon pledged Sunday to do what's necessary to prevent fuel shortages, saying the government won't allow such shortages to hurt the French economy. The head of France's petroleum industry body said fuel reserves were "enough to keep us going for a few weeks."

The protests in France come as countries across Europe are cutting spending and raising taxes to bring down record deficits and debts from the worst recession in 70 years. Labor leaders, students and civil servants are fighting back.

French truckers staged organized slowdowns Monday to snarl highway traffic. Cars and trucks drove at a snail's pace on the main highway between Paris and the northern city of Lille, with red union flags waving out the windows.

Youths, meanwhile, burned tires and cars, set up blockades and clashed with riot police Monday outside some high schools in Paris and nearby suburbs.

Students from Lycee Joliot Curie in the Paris suburb of Nanterre tried to blockade their school, with about 100 facing off against police, who responded with rubber bullets. In all, 261 schools were blocked by protests Monday.

Rail unions, which have been on strike since early last week, prolonged their walkouts through Tuesday to coincide with more than 200 street protests -- the sixth nationwide protest since early September.

Union leaders also called for support strikes from other sectors, including energy, postal workers and private commerce, as well as from employees at Eurotunnel, which runs freight and passengers under the English Channel to London.

France's DGAC civil aviation authority ordered airlines to cancel 50 per cent of their flights Tuesday out of Paris' Orly airport, and 30 per cent at other airports nationwide, including Paris' largest airport, Charles de Gaulle. Most disruptions were expected to hit short- and medium-haul flights.

Airport operator ADP said strikes by oil workers at Charles de Gaulle airport had already begun causing delays on Monday. Spokesman Jerome Landras said travelers should contact their airline to check on flights.

Train traffic also continued to suffer from the nearly weeklong strike. France's SNCF railway operator said about half its high-speed TGV trains had been canceled Monday, but traffic on the Eurostar between Paris and London was normal.