Mr Macron’s reforms would raise the minimum retirement age from 62 to 64.

His government forced the bill through parliament last month, without a vote, by means of an executive power.

Judges of the Constitutional Council were last night placed under police protection over fears they would be attacked. Officers were deployed at the court, in the centre of Paris, as a temporary ban on protests outside of it came into force and will not be lifted until tomorrow morning.

A police note leaked to the media said: “There exists a serious risk that determined radical elements of high potential violence form unauthorised marches in this sector.”

Some 380,000 people demonstrated yesterday across France, according to the country’s interior ministry. The unions, however, put the figure at more than a million.

The court will hand down two decisions by the end of today. The nine-member council will first rule on whether the reform is constitutional. It is thought that judges will partially approve the bill.

Secondly, it will look at two separate requests from the left-wing opposition to launch a referendum on a different law that would actually limit the retirement age to 62.

“The decision from the Constitutional Council on Friday will bring an end to the democratic and constitutional procedures,” Mr Macron said during a trip to the Netherlands on Wednesday.