Macron defied fierce trade union opposition and weeks of sometimes violent protests against his plan to raise the retirement age by two years to 64, ramming the legislation through parliament without a final vote and signing it into law last month.

The council said in a statement that the proposed referendum did not meet the legal criteria as defined in the constitution.

Since Macron bypassed parliament, opposition lawmakers have turned to the Constitutional Council twice in an attempt to derail the reform, seeking its approval on each occasion for a referendum on the retirement age.

The council's role was to decide whether the opposition's request met the legal conditions for a referendum.

A first attempt had already been struck down, partly because the pension bill had yet to be enacted and the proposed referendum would not have led to a change in the law.

Macron says the French must work longer or else the pension budget will fall billions of euros into the red each year by the end of the decade.

But the pension system is a cornerstone of France's cherished social protection model and labour unions say the money can be found elsewhere, including by taxing the rich more heavily.

Unions, and the opposition, will now turn their attention to a nationwide day of protests scheduled for June 6, two days before lawmakers discuss an opposition motion to annul the pension legislation.

While attention has focused on the retirement age of 62, only 36% of French workers retire at that age and another 36% already retire older on account of requirements to pay into the system for longer to be able to claim a full pension.

Nonetheless, French pension payments as a share of pre-retirement earnings are substantially higher than elsewhere, OECD figures show.

Opinion polls show a vast majority of voters reject the new law.