Emmanuel Macron's government is facing a confidence vote next month after the president failed to win an outright majority in Sunday's legislative elections.
France’s left-wing Nupes alliance said on Monday that it plans to put forward a no-confidence ballot against Mr Macron's Ensemble grouping on 5 July.
Nupes is the second-biggest grouping in the lower house of parliament, following Sunday’s election, but does not have enough votes on its own to get the no-confidence vote adopted, and has few allies in a very fragmented parliament.
Mr Macron was on Monday scrambling to seek support from parliamentary rivals in order to salvage some of his reform agenda and avoid political paralysis, after voters punished them on Sunday
While the "Ensemble" grouping secured the largest number of lawmakers in the 577-seat National Assembly, it fell well short of an absolute majority in a vote on Sunday that saw a leftwing alliance and the far-right perform very strongly.
There is no script in France for how things should unfold.
"It's going to be complicated," government spokeswoman Olivia Gregoire told France Inter radio. "We're going to have to be creative.
"What I fear most is that this country be blocked," she added.
Macron himself has yet to comment on the election result.
One key question is whether he will try to strike a coalition deal with the conservative Les Republicains - who have for now rejected that option - or enter into messy negotiations with opponents on a bill-by-bill basis.
"We will try to bring others on board with us, especially to convince the few moderates in parliament to follow us," Gregoire said, adding that Macron is set to reshuffle his government in the coming days.
If no agreement can be found, the euro zone's second biggest economy faces political paralysis.
Parliament is fragmented, with a broad leftwing alliance and, diametrically opposed to it, the largest far-right group ever elected.
If Mr Macron cannot find enough support to make things work, France may face snap elections down the line.
A first major test will be a cost-of-living bill which Gregoire said the government will put to lawmakers in eight days, when the new parliament will sit for the first time.
Over the summer, proposals on renewable energy will test the solidity of Jean-Luc Melenchon's broad leftist alliance.
Final figures showed Macron's centrist camp got 245 seats - well below the 289 needed to control parliament, the Nupes leftwing alliance 131, the far-right 89 and Les Republicains 61.
