New French President Emmanuel Macron's government has reaffirmed its plan to boost the representation of smaller parties in parliament as its predicted majority after this weekend's run-offs grew, and likely voter turnout shrank.

Three opinion polls ahead of Sunday’s second round of legislative elections indicated that the upstart centrist President and his one-year-old En Marche! party would win 80 per cent or more of the seats in the lower house.

Those were the highest predictions of the campaign to date.

Macron's opponents, still smarting from his presidential victory just over a month ago, warn that such a majority in a country with obvious and deep political divisions is a threat to democracy.

An En Marche! dominance of parliament would be the biggest in decades by any party, even though it gathered only about a third of votes in round one.

Over half of the electorate did not vote, and many said they saw no point in doing so. The latest polls indicated that even fewer would turn out in round two.

France's two-round voting system, used in all types of elections including the presidential contest that brought Macron to power, eliminates low-scoring candidates after the first round.

Thanks to this system, and to electoral pacts aimed at keeping far-right Front National candidates out of parliament, the FN looks set to get only a handful of seats in the National Assembly, even though its leader Marine Le Pen won the support of a third of voters in the presidential election.

Some surveys indicate that she may even be the only FNt member in the 577-seat assembly.

Left and far-left lawmakers are also expected to be few in number.

“We will ask parliament to work on this subject,” technology minister Mounir Mahjoubi said on France 2 television.

“By introducing a dose of proportional representation, parties that get such [low] scores would have more representation. That would be fairer, and above all it would improve debate.”

Polls by Opinionway and Harris Interactive on Thursday had En Marche! and its centre-right Modem ally winning between 440 and 470 seats in the lower house, a majority unseen since conservative president Charles de Gaulle took over 80 per cent of seats in 1968.

A poll by Odoxa published on Friday, the last day of campaigning, put them on 430 to 460 seats.

Macron has promised to push through pro-business labour reforms that go beyond those he was involved in as economy minister in the Socialist government of 2012 to 2017.

While the proposals have been part of his appeal to the broader electorate, and are welcomed in French business circles, they are deeply unpopular with some sections of society who fear erosion of workers' rights.

Controversy over the subject resulted in strikes and street protests last year, tore the then-ruling Socialist party apart, and helped cause its disastrous election showings this year.

Jean-Luc Mélenchon, a far-left candidate backed by a fifth of the electorate in the presidential vote, is set to be one of the few left-wing lawmakers to sit in the new parliament.

On Friday, he said Macron should not expect an easy ride.

“If you believe the workers of this country and salaried employees generally are going to be fleeced simply because all the glossy magazines have published a smiling photo of the young prince [Macron], you are dreaming,” he said on Europe 1 radio.

“This is France, and a century and a half of struggle for the rights enshrined in the labour code are not going to be wiped out at the stroke of a pen. There will be a struggle.”