The protest march in Paris was closing in on the Constitutional Council's headquarters, opposite the Louvre museum in central Paris, which was protected by a phalanx of anti-riot police in full body armor brandishing shields.
Demonstrators also stormed the headquarters of French luxury goods firm LVMH in Paris, while there also were protests in other parts of the nation.
Police Thursday expected fewer than half the nearly 1.3 million who demonstrated in March at the height of the protests against the reforms, which include raising the retirement age from 62 to 64.
All eyes on Friday will turn to the Constitutional Council, the country's highest administrative authority, which will announce its verdict on the pensions legislation in the final hurdle before Macron can sign it into law.
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 leader said he would invite labor representatives for discussions once the court decision was published.
"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."
Paris police have banned any demonstration around the Constitutional Council until Saturday morning.
Surveys show that about two in three French people are against the pension changes, but Macron argues that they are essential to stop the system falling into heavy deficit in coming decades.
Critics accuse the president of riding roughshod over public opinion and parliament, where the minority government invoked controversial executive powers to ram the legislation through without a vote at the end of March.