France is set for disruption to transport and public services, as unions protest against plans to raise the pension age from 62 to 64.
Most train and metro services are cancelled on Tuesday, and many schools will be closed.
It is the sixth day of strikes and protests since mid-January, and unions say it will be the biggest yet.
More than one million people are expected at demonstrations in Paris and other cities.
With the government showing no sign of backing down on its pension plan, one union leader has said there is talk is of escalation and “bringing the country to its knees”.
In the days ahead, there will be calls to extend the strikes in key sectors like power generation and gas terminals.
So far, for all the noise and sporadic disruption, the campaign has caused little damage to the economy, and in the meantime the bill is proceeding through parliament.
Unions and the left know time is running out before the reform becomes a fait accompli – which is all the more reason for them to up the pressure now.
The majority of French citizens back the ongoing strikes against President Emmanuel Macron’s pension reform, a poll by French survey group Elabe suggests.
According to the opinion poll, 56% of people support rolling strikes and 59% back the call to bring the country to a standstill.
Two-thirds of people support the protest movement against the government’s planned pension reforms in general, the poll indicates.
President Macron has called the reform “essential” because of deficits forecast for France’s pension system over the next 25 years, according to analysis by the independent Pensions Advisory Council.
Government spokesman Olivier Véran told France 2: “We don’t want French people to be, quote, unquote, ‘victims’ of a long-term blockade.”
Last week, he warned that the strikes could lead to an “ecological, agricultural and health catastrophe”.
More than 260 demonstrations are expected across France on Tuesday, with up to 1.4 million people expected to attend, a police source told AFP news agency on condition of anonymity.
Neighbouring European economies have already raised the retirement age to 65 or above to reflect longer life expectancy.