France goes to the polls on Sunday in the first round of parliamentary elections, with a resurgent and newly unified left seeking to thwart President Emmanuel Macron's plans for reform.
Elections for the 577 seats in the lower house National Assembly are a two-round process. The shape of the new parliament will become clear only after the second round, a week later, on June 19.
Polls open in mainland France at 8:00 am (0600 GMT), after voters in overseas territories cast ballots earlier in the weekend.
After a dismal performance in April, the French left has unified in a coalition for what its leader Jean-Luc Melenchon dubs "the third round" of the presidential elections.
Opinion polls show the president's centrist alliance, Ensemble (Together), and Melenchon's NUPES coalition of hard left, Socialists, Communists and Greens neck-and-neck in the popular vote.
But France's constituency-based parliamentary system and the two-round election means that the seat breakdown will be another matter, and much will depend on turnout in the second round.
The abstention rate is predicted to be well over 50 percent in the first round, in what would be a new record for elections already marked by feeble participation in recent years.
If the president's alliance retains an overall majority, Macron will be able to carry on governing as before.
Falling short could prompt messy bill-by-bill deals with right-wing parties in parliament or an unwanted cabinet reshuffle.
A win by the left-wing alliance -- seen as unlikely by analysts but not impossible -- would be a disaster for Macron.
It would raise the spectre of a clunky "cohabitation" -- where the prime minister and president hail from different factions -- which has paralysed French politics in the past.
The most recent example was from 1997 to 2002 when right-wing president Jacques Chirac ruled in tandem with Socialist Lionel Jospin as premier.
Socialist president Francois Mitterrand twice had to cohabit with right-wingers: with Chirac in a famously fractious ruling duo and then with Edouard Balladur.
Melenchon, a former Marxist, has already made clear his ambition to become prime minister and stymie Macron's plan to raise the French retirement age, although the president would retain control over foreign policy.
- 'Strong and clear majority' -
Stepping into the fray on Thursday, Macron acknowledged the stakes were high, warning France against choosing "extremes" that would add "crisis to crisis".
"If the presidential election is crucial, the legislative election is decisive," he said on a visit to the rural Tarn region, calling for a "strong and clear majority".
Polls have indicated that Macron's alliance is expected to win the largest number of seats but is by no means assured of getting over the line of 289 for an absolute majority.
Analysts say the young and members of low-income groups are among those likely to stay at home for the first round and if Melenchon could mobilise them for round two it would transform the picture.
While Macron and his European Union allies breathed a heavy sigh of relief after his solid, if unspectacular, presidential victory against far-right leader Marine Le Pen, the last weeks have brought no sense of a honeymoon.
Energy and food prices are soaring in France as elsewhere in Europe, the treatment of English fans at the Champions League final in Paris damaged France's image abroad and Macron has been accused by Ukraine of being too accommodating to Russia.
His new Disabilities Minister Damien Abad has faced two rape accusations -- which he has vehemently denied -- while new Prime Minister Elisabeth Borne has yet to make an impact.
Macron has made clear that ministers who are standing in the election -- including Borne, who is making her first attempt at winning a seat -- will have to step down if they lose.
Of the 577 lawmakers in the National Assembly, eight represent France's overseas territories and 11 account for French nationals living abroad.
Macron's party and his allies currently hold an absolute majority of 345 seats.
Under France's system, a candidate needs over half the vote on the day as well as the backing of at least 25 percent of registered voters in a constituency to be elected outright in the first round.
Otherwise the top two candidates in a constituency, as well as any other candidate who won the backing of at least 12.5 percent of registered voters, go forward to the second round, where the candidate with the most votes wins.