PARIS (AP) -- French voters are casting ballots Sunday in the final round of parliamentary elections that could clinch President Emmanuel Macron's hold on power, as his fledgling party appears set to rout mainstream rivals and turn politics as usual on its head.
 
Pollsters say that after its dominant performance in last week's first-round vote, Macron's Republic on the Move! party could win up to 450 seats Sunday in the 577-seat National Assembly, the powerful lower chamber.
 
If the steamroller effect continues for Macron's party, half of whose candidates are women and the other half new to politics, France will have a chamber of representatives like few others, fulfilling the president's wish to renew a political class dominated by career politicians, peppered with corruption and losing credibility.
 
The strong mandate would also give the 39-year-old president a free hand to move fast with promised legislation, notably on changing labor laws to make hiring and firing easier.
 
That prospect worries both rivals and some voters, and makes the turnout rate critical. A healthy participation rate might dampen the expected victory of Macron's party.
 
At midday, turnout appeared to be lagging. The Interior Ministry said just 17.8 percent of voters had cast ballots, down from 19.2 percent at the same time during the first round, and 21.4 percent at the same time during the second-round voting in the last parliamentary elections in 2012.
 
Less than half the 47.5 million-strong electorate turned out to vote last Sunday, a record low that especially punished the once-feared far-right National Front party of Marine Le Pen, runner-up to Macron for the presidency.
 
Candidates from the conservative party, The Republicans, are expected to form the largest opposition group, with 70-110 seats, according to pollsters, with other parties sharing the rest.
 
The Socialists, who dominated the outgoing Assembly with 314 seats, but were flattened under the unpopularity of former President Francois Hollande, could win as few as 20 seats.
 
Macron's party has 513 candidates vying for 573 seats. Four seats were won outright in last Sunday's first round.
 
Concern that opposition voices might be silenced, and pluralism allegedly diminished, by a massive pro-Macron legislature were reflected in a poll published Thursday by Elabo for BFM-TV suggesting that more than half of respondents hoped the second round would "rectify the first round with a less large majority than expected."
 
"This is France, not Russia," far-left candidate Jean-Luc Melenchon said Friday on Europe 1 radio. "We're going to find ourselves with fewer opposition representatives than there are in Russia." While Melenchon is known for bold talk, his words underscored worry about an eventual all-powerful Macron who, Melenchon said, "is going to end up believing he walks on water."
 
While French voters have handed past presidents large majorities in parliament, what's different this time is that Macron's party is splitting _ and therefore weakening _ the opposition.
 
Some voters seemed excited by a victory for Macron's party, while others were frustrated.
 
Parisian voter Olivier Palate said the success of Macron's party was like a "tidal wave. Now I think that for the second round we no longer have too much choice."
 
The party of Melenchon, a candidate in a Marseille district facing off a Macron candidate, was also hit hard by the low turnout rate. But his alliance with the French Communist Party could end up giving them more seats than Le Pen's National Front _ even if her party gets more votes.
 
The voting system punishes parties outside the mainstream, or with no mainstream allies, like Le Pen's National Front.
 
The party is expected to win only a handful of seats despite its third-place showing in the first round. The populist Le Pen, running for a parliamentary seat to represent her northern bastion around Henin-Beaumont, appears likely to win after scoring 46 percent of the vote in the first round.
 
The National Front had two seats in the outgoing parliament and the only lawmaker seeking to renew his mandate, Gilbert Collard running in the southern Gard region, could lose. His opponent, a former bullfighter representing Macron's party got a public boost this week from visiting Prime Minister Edouard Philippe.