What's next for France's pension reform?

France's Constitutional Council is due to deliver its verdict on Friday on a deeply unpopular bill which will delay retirement by two years to 64, and on plans for a referendum to challenge it.

Here is why this matters and what could happen:

VERDICT ON THE PENSION BILL

* The Council can strike down the bill altogether if it considers it breaches the Constitution. Opposition parties have asked it to do so, for choosing to tack the pension reform onto a social security budget bill, setting a tight deadline on debates and then bypassing a final vote in parliament.

This would be a stinging defeat for President Emmanuel Macron and a surprise win for unions and protesters. Macron would have the option of starting from scratch with a new bill or moving on.

However, constitutional experts - and government sources - say the Council is unlikely to block the overall reform, which it has rarely done in the past.

* If the Council sees nothing wrong, the government could enact the legislation in the coming days, which officials hope would progressively put an end to protests.

* Alternatively, and more likely constitutional experts and government sources say, is that the Council approves the raising of the legal retirement age, but strikes down some measures designed to boost employment for older workers on the grounds that they do not belong in a social security budget bill.

REFERENDUM

Even if the Constitutional Council gives its green light - with or without caveats - this may not be the end of the road.

Opposition Parliament members want to organise a so-called citizens' referendum on capping the retirement age at 62.

To do so, they would need to jump through hoops that have so far prevented one from being organised in France since the concept was introduced in 2015.

The first step - having enough backing from members of Parliament - is already met. The second is getting the Council's green light.

But then, the next condition is getting a tenth of registered voters to sign a petition calling for the plebiscite.

That is a tall order, and must be achieved within nine months. Some unions have asked the government not to publish the law before that deadline has lapsed.

If the threshold is met, the Senate and Assembly have six months to examine the proposal to cap the retirement age to 62. If Parliament does not respond, the president must submit it to referendum.