PARIS >> President Emmanuel Macron’s barely year-old party is set to upend politics as France knows it. But the rosy glow of a likely massive victory in next Sunday’s final round of French legislative elections could be dimmed without a robust opposition to debate controversial initiatives like far-reaching labor law reforms that scare some, anger others and risk sending those who want none of it into the streets.

France’s new leader, at 39 the youngest-ever and just getting his feet wet in politics, aimed from the start to remake the political landscape, much of it populated with old- school career politicians. Based on results from Sunday’s first-round of voting, he is shattering it.

His fledgling Republic on the Move — fielding many candidates with no political experience — won 28 percent of the vote, putting it on course to take as many as 450 seats in the powerful 577-seat National Assembly, an unprecedented feat in France. Opponents occupying the remaining seats would represent a fragmented opposition, most without the 15 seats needed to even get speaking time, funding or other ways to weigh on policy.

Macron’s party decimated the Socialist Party that governed France for the past five years and got less than 7.5 percent of Sunday’s vote. It flattened the far-right National Front whose leader, Marine Le Pen, was vying with him for the presidency last month. The party got just over 13 percent of the vote. Macron’s closest rival, the mainstream conservatives, took less than 16 percent.

Such a parliament would be the most “monochrome of the Fifth Republic,” said Frederic Dabi of the Ifop polling firm, speaking on CNews TV.

But another figure also stood out — the record-low voter turnout. Less than half of France’s 47.5 million electorate cast ballots.

The Le Figaro daily warned against the “optical illusion” created by the apparent sweep, noting in a commentary that with less than one in two voters casting ballots and a voting system that favors large political parties, the count racked up by Macron’s party “is far from equaling support.” Macron himself was massively elected on May 7 in large part to keep his rival, Le Pen, from power.

“I’ll make their lives hell in the Assembly,” declared Jean-Luc Melenchon, the far-left leader whose presidential bid failed — and who, after Sunday’s vote, had a comfortable lead in his bid for a parliamentary seat.

Macron intends to set his reform agenda into motion within weeks and has called a special parliamentary session next month to kick-start the process. This includes plans to change French labor laws to make hiring and firing easier — reforms he intends to push through using a system, also used by previous governments, that calls for a measure to be quickly ratified by parliament without an extended debate and no opportunity to amend it.

But Macron is already being warned he will not have carte blanche.

Some unions and a collective, the Social Front, formed to combat Macron’s policies, plan a rally next Monday outside the National Assembly to protest Macron’s plans to reform the labor law and skirt normal procedure to pass changes.

With a super-majority all but assured in the legislature, “the opposition to Macron … will be in the street,” said Hall Gardner, chair for International and Comparative Politics at American University of Paris and a long-time observer of the French political scene.

“Any system that doesn’t use checks and balances is dangerous,” Gardner said. “If he’s smart he will use the National Assembly and let them moderate the law somewhat. … But I think he really wants to shake up the labor system.”

Macron’s electoral success has boosted the morale of France’s European neighbors. They, along with foreign investors, are watching to see whether Macron follows through on his pledge to loosen French labor laws and reduce the power of unions, moves he says will help create jobs and inject new confidence into the Europe-wide economy. The past three French presidents also promised labor reforms but failed to make dramatic or lasting change, and France’s economy has lagged behind and its jobless rate remains stuck around 10 percent.

Macron also wants to reinvigorate cooperation among the 27 members of the European Union in the wake of Britain’s Brexit vote, notably by joint military spending and a shared budget for the countries that use the euro.

At Wednesday’s Cabinet meeting, he is to introduce plans to clean up politics, to staunch the steady flow of scandals that have over decades reduced voter trust in the French political class. New terrorism legislation is to be presented on June 21 to make some security measures permanent and to extend the current state of emergency beyond July, when it is set to expire. Last week, he formally presented a “national center of counterterrorism” to be based at the Elysee Palace.

Only four seats were decided in Sunday’s first round of voting, and some powerful figures fell, including the Socialist Party leader, Jean-Christophe Cambadelis, and the Socialists’ presidential candidate, Benoit Hamon.

Le Pen, who had Europe on edge until she lost the presidential race, was trying to save herself and her party in the legislative contests. She herself made it to the second round in her northern bastion of Henin-Beaumont, but some ranking party members were eliminated outright, notably campaign director Nicolas Bay, the party’s secretary-general.

Francois Fezeau is among those happy with the outcome. The 29-year-old Parisian said the election results “fill me with enthusiasm.”

“We had a recent (presidential) election that shook up the traditional parties and I think that the legislative elections give Macron the possibility to show what he is able to do,” Fezeau said.