French unions and president Nicolas Sarkozy go head to head again today in the continuing row over his plans to raise the retirement age.
Train drivers launched an open-ended strike and will be joined by workers from throughout the economy tomorrow.
Both groups are angry at a pension reform the Senate is expected to pass by the week's end.
Street protests also are being planned by unions tomorrow and Saturday. Last month, similar action brought a million people on to the streets.
After months of battle over raising the retirement age by two years, this could be the decisive week, and some unions upped the stakes by declaring open-ended strikes this time, meaning they could last for days. Past walkouts lasted only one day.
For Mr Sarkozy, the contest is about principle. His conservative allies say that faced with gaping budget deficits and sluggish growth, France must get its finances in better order. Even with the two-year change France would still have among the lowest retirement ages in the developed world.
Unions fear the erosion of the cherished workplace benefit, and say the cost-cutting axe is coming down too hard on workers.
Mr Sarkozy's government is all but staking its chances for victory in presidential and legislative elections in 2012 on the pension reform, which the president has called the last major goal of his term. France's European Union partners are keeping watch, as they face their own budget cutbacks and debt woes.
Early forecasts suggested that railway services, schools, oil refinery production and public transport could be curtailed.
Today French civil aviation authorities urged airlines to cancel 30% of flights at Paris' Charles de Gaulle airport and 50% at Orly airport because of expected staff shortages. The rail authority expects just one train in three on the high-speed TGV lines, and the Paris Metro is expecting widespread disruptions.
One risk for the government is that students, who would not be affected by the retirement reform for decades, could join the marches out of sympathy for workers.
Mr Sarkozy has backed down from at least two reforms planned in education, opting not to incur students' anger. Potent student-labour coalitions have brought down many planned government reforms over the years in France.
The Education Ministry predicted today that more than one in four elementary and nursery teachers would stay home tomorrow, although one union representing those teachers countered that nearly half would.
However cracks were emerging within the labour front.
UNSA-Transport, a union representing Paris transit workers, could not muster enough support for calls for the open-ended strike, with a spokesman saying that "a certain fatigue" had set in among its rank-and-file.
The new nationwide strikes will be the fifth since May, including two last month.
The lower house of parliament, the National Assembly, approved the reform last month. The Senate has approved the article on raising the retirement age from 60 to 62, but is still debating the overall reform. The bill also raises the age of eligibility for a full pension from 65 to 67.