After years in the political wilderness, France's centre-left Socialists have returned as power brokers who will determine the fate of both Emmanuel Macron's new prime minister and several of his business-friendly reforms.
Premier Sébastien Lecornu will try to woo Socialist leaders at their first meeting on Wednesday, with the party having become a swing voting bloc in a hung parliament that has toppled two prime ministers over the past year.
Lecornu needs them to abstain in a vote on the 2026 budget to avoid the fate of his two predecessors who failed to muster support for their own deficit-cutting efforts.
But Socialist party chief Olivier Faure is determined to drive a hard bargain, telling France TV earlier this week: "He will have to choose between what the [right-wing] and the bosses are telling him and what we're telling him: namely, we need social justice, tax justice, committing to the green transition and improving the lives of the least well off."
Although the Socialists only hold 66 seats in the 577-strong National Assembly -- less than half of the number of lawmakers in Macron's camp or in Marine Le Pen's far-right opposition -- they are demanding a steep price for their support.
They want to halve the budget cuts of €44bn proposed by Lecornu's predecessor François Bayrou, and unpick policy achievements that Macron sees as central to his legacy.
This includes suspending his hard-fought pensions reform that raised the retirement age by two years to 64, and pushing for much a bigger wealth tax than the one Macron scrapped early in his first term.
Lecornu, the only minister to have served continuously in government since Macron was first elected in 2017, has already signalled openness.
He quickly binned Bayrou's deeply unpopular proposal to scrap two national holidays and is sounding out opposition parties before forming a government.
"It will be difficult but necessary to give the country a budget," Lecornu told regional papers last weekend.
The prime minister's high-stakes talks come ahead of expected widespread protests and strikes on Thursday organised by labour unions. Failure to placate the Socialists could prove terminal.
An Élysée official said that, if the Socialists help oust another prime minister, Macron could call snap elections again, as he did in 2024.
"If he refuses to change direction, or only in a tiny way, we will vote him out just like his predecessors," warned Stéphane Troussel, a socialist politician and head of the Seine Saint-Denis area, north of Paris.
However, some party officials acknowledge that pushing their advantage too far carries risks.
Socialists can ill-afford to alienate their leftist voting base by endorsing Macron's unpopular proposals to freeze spending on pensions and benefits. But they are also at risk if Lecornu falls and Macron calls another legislative election, in which they could lose seats as the far-right advances.
Another test is coming up in local elections in March, when far-left allies-turned-rivals are gunning to unseat them in mayoralties including Paris, Lille, and Rennes.
Politicians within Macron's camp believe the Socialists can be persuaded with some concessions, as they were earlier this year when they allowed Bayrou to pass a slightly watered-down 2025 budget originally proposed by his predecessor, Michel Barnier.
"Each of us has a powerful card in hand -- we can dissolve parliament, which [the Socialists] do not want, and they can topple the government, which we do not want," the person said.
After decades as one of France's main governing parties, the Socialists were nearly obliterated in 2017 when Macron -- a former minister from their ranks -- won the presidency as leader of a new centrist movement challenging the establishment.
Faure has staked his party's revival on moving it further left and sealing an uneasy electoral pact with far-left firebrand Jean-Luc Mélenchon.
Éric Coquerel, a lawmaker from Mélenchon's La France Insoumise (LFI), said the Socialists would be punished by voters if they enabled Lecornu.
"If they help him, I think it's suicidal. [The government] will fall very quickly and, at the next elections, it will be a political suicide for the PS," he told the FT.
Higher taxes on the rich have emerged as a priority for the Socialists.
They want to enact an unprecedented tax advocated by left-wing economist Gabriel Zucman, which would apply to people with a net worth exceeding €100mn. They would pay an annual levy of at least 2 per cent on all types of assets, including companies they own or shares they have in them.
The left claims this would raise €15 to €20bn a year. But critics put the figure closer to €5bn and warn that the Zucman tax is potentially unconstitutional, unworkable, and would hobble start-ups such as artificial intelligence company Mistral, since it could force founders to sell shares to pay the tax.
Socialist MP Philippe Brun said the rate and parameters of how the tax is calculated could be discussed, but insisted that the rich needed to shoulder efforts to tackle the deficit.
Brun said that the working and middle classes needed to be shielded from spending cuts. "We demand more tax justice with contributions from those who have been spared in recent years, especially the ultra-wealthy," he said.
Lecornu, his right-wing allies Les Républicains and Macron himself are unlikely to sign up to a full-blown Zucman tax. But some of them have signalled openness to making the wealthy contribute more.
Bruno Cautrès, a political scientist at Sciences Po university, said the government may make "some concessions" but added: "Macron will never allow a Zucman tax. It's too at odds with what Macron has wanted since 2017."