Many parents will have to look after their children as 70 percent of primary school teachers are expected to strike and many schools will close entirely for the day, according to the main teachers' union.
Philippe Martinez, head of the hard-left CGT union, said he hoped for "lots of people in the street and lots of people on strike".
He told broadcaster France 2 that he expected many in the private sector to join with public-sector workers, with "in certain big companies, striker rates that should hover around 60, 70 percent".
The unions are hoping for over a million demonstrators in more than 200 cities across France.
French media have reported that police are making plans for 550,000 to 750,000 protesters, including 50,000 to 80,000 in Paris.
Interior minister Gerald Darmanin said Wednesday that 10,000 police and gendarmes would be on alert, more than a third of them in the capital, including to look out for some 1,000 demonstrators who could be "violent".
Transport minister Clement Beaune has warned it will be "a hellish Thursday", urging all those who can to work from home.
With Paris metros and buses in disarray, basketball fans could encounter trouble as they try to reach the sold-out NBA Paris Game between the Detroit Pistons and Chicago Bulls in the northeast of the city.
Macron in Barcelona
Opinion polls show that around two-thirds of French people oppose raising the retirement age, a move that comes amid high inflation and with the country still recovering from the Covid-19 pandemic.
Macron's last attempt at pension reform in 2019, aborted a year later when Covid-19 hit Europe, prompted the longest strike on the Paris transport network in three decades.
The 45-year-old centrist vowed to press ahead with plans to push back the retirement age during his successful re-election campaign last year, pointing to forecasts that the system could fall into heavy deficits at the end of the decade.
France's current retirement age is one of the lowest in the European Union.
But unions are suspicious of the new overhaul, eager to protect those who started working at a young age or have been toiling in physically demanding jobs.
Prime minister Elisabeth Borne has defended the reform, still to be debated in parliament, as a way to ensure more "justice" for retirees.
"Four out of 10 French people, the most fragile, those of the most modest means, those who have tough jobs, will be able to retire before 64 years old," she has told parliament.
Macron, however, will not be in France on Thursday.
He and nine ministers will be attending a French-Spanish summit in Barcelona, though labour minister Olivier Dussopt will stay behind.
In 2010, more than a million people protested against the plan to raise the retirement age to 62, according to police figures, but the bill proposed by the right-wing government of president Nicolas Sarkozy was passed anyway.