Hundreds of thousands of people are set to take to the streets across France again Thursday to protest against President Emmanuel Macron's pension reforms, in a final day of demonstrations before a crucial court decision on the legislation.

Police expect around 400,000 to 600,000 people to take part nationwide. That would be fewer than half the nearly 1.3 million reached in March at the height of the protests against the reforms, which include raising the retirement age to 64 from 62.

Nevertheless, "Now's not the time to give up, because that's what Macron is expecting", said Johan Chivert, a student in the Creuse region in central France.

"We have to keep going and show the people are against this reform."

Security forces are on alert for troublemakers, with around 1,500 anarchist and radical protesters expected in Paris, while regional towns such as Nantes and Rennes are again seen as being at risk of clashes.

All eyes are currently on the constitutional court, which is due to rule on the legality of the draft pensions law.

"The decision from the constitutional court on Friday will bring an end to the democratic and constitutional procedures," Macron told reporters on a trip to the Netherlands on Wednesday, adding that public debate "will continue, for sure".

If the court issues a green light -- as ministers are privately confident it will -- Macron hopes to sign the changes into law immediately, clearing the way for them to enter into force before the end of 2023.

Having repeatedly snubbed calls for talks with union leaders in recent weeks, the 45-year-old said he would invite labor representatives for discussions once the court decision was published.

"I know that traces of our current disagreements will remain but I will do it (call for talks) in a spirit of concord and with the desire to look to the future, whatever decision is announced," he added.