* Protesters to march in Paris from 1200 GMT
* March against Macron's labour reforms
* Polls show far-leftist Melenchon as strongest opponent
* Majority consider Melenchon would not be good president

French far-left opposition leader Jean-Luc Melenchon‏ is rallying his supporters in Paris on Saturday against Emmanuel Macron's labour reforms, in a test for both men that could be key to the implementation of the centrist president's policies.

‘We won't let them empty the poor's pockets to feed the rich!’ Melenchon's 'France Unbowed' party said in leaflets distributed before the 2 p.m. (1200 GMT) march against what the admirer of late Fidel Castro calls a ‘social coup d'etat.’

Rallies organised by unions against the same labour reforms giving companies more power to set working conditions seem to be losing steam, but France Unbowed are hoping for a show of force to reinforce opinion polls showing Melenchon as Macron's strongest opponent.

‘Emmanuel Macron has started an arms-wrestling contest with the French people ... but I think we can stop those (labour reform) decrees,’ France Unbowed lawmaker Adrien Quatennens told Reuters, saying their aim was to convince people who are not used to taking to the streets to join the protests.

Party officials said about 150 buses will bring protesters from all over France to take part in the Paris rally.

The new labour rules, discussed at length in advance with unions, will cap payouts on dismissals that are judged unfair, while also giving companies greater freedom to hire and fire employees and to agree working conditions.

A string of opinion polls showing Melenchon is seen as the strongest opponent to Macron highlight the weakness of mainstream opposition, with the Socialists, who ruled France over the past 5 years, in tatters, the conservative The Republicans divided over whether to back Macron, and the far-right National Front split by internal fighting.

Ironically, Melenchon's strength could be a good thing for Macron, because polls also show he is not seen as a credible alternative but rather a strong voice on the protest front.

An Odoxa survey carried out this week showed 66 percent of voters considered Melenchon would be a bad president.

That rating, however, improved by six percentage points over the past year and Melenchon is more popular among the youth.

Macron and his government have repeatedly said they would not bow down to pressure from the street, but they are likely to monitor closely how many people take to the streets on Saturday.

The centrist president formally signed the labour decrees on Friday. They are due to enter into force by the start of next year.

The measures are only the first step of a series of reforms that will also amend the unemployment benefits and pension systems, changes that could well provoke more protests than changes to the labour code.