France's lower house voted by a large majority in favour of President Emmanuel Macron's bill designed to tighten the country's immigration rules, despite concerns it could cause a rebellion from left-leaning members.
The bill won the backing of the far-right National Rally under Marine Le Pen, but in the end it did not need the party's support to push it through.
Mr Macron's government regards the legislation on tightening immigration rules as crucial to taking control of the issue from the far right.
The bill has undergone many amendments that have further tightened it from when it was originally submitted, with the left accusing the government of caving in to pressure from the far right and submitting to its agenda.
"We can rejoice in ideological progress, an ideological victory even for the National Rally [RN], since this is now enshrined into law as a national priority," said Ms Le Pen, a three-time presidential candidate.
The RN had previously said it would vote against the bill or abstain.
French media dubbed her surprise move a "kiss of death" for Mr Macron's party.
Ms Le Pen, who now leads the RN's politicians in parliament but is widely expected to stand again for president in 2027, described the legislation as a "toughening of immigration conditions".
Her announcement came after a commission of upper house senators and lower house MPs agreed on a new draft of the bill, which was voted down without being debated in the National Assembly last week in a major blow to Mr Macron.
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While the government had the numbers for the legislation to be passed, there are concerns in Mr Macron's camp that there could be a rebellion from within its own ranks.
Prominent left-leaning Renaissance MP Sacha Houlie said he would vote against the legislation and called on others to follow him, with some sources saying 30 pro-Macron MPs could do so.
In a sign of the seriousness of the situation, Mr Macron called a meeting of his ruling party at the Elysee Palace ahead of the vote, party sources told AFP.
According to a participant at the meeting, Mr Macron said he would submit the bill to a new reading rather than promulgate it if it were passed only with the help of the votes from Ms Le Pen's RN.
Health Minister Aurelien Rousseau, Higher Education Minister Sylvie Retailleau and Housing Minister Patrice Vergriete met Prime Minister Elisabeth Borne and warned they could resign, sources told AFP.
Interior Minister Gerald Darmanin, the ambitious 41-year-old who has led the legislation, warned on Sunday that Ms Le Pen could win the 2027 presidential election if the bill is not passed.
The left has reacted with horror to the prospect of the legislation being passed, with the head of Socialist politicians in the National Assembly, Boris Vallaud, describing it as a "great moment of dishonour for the government".
Passing the legislation is also critical for Mr Macron who cannot stand again in 2027 after two consecutive terms and is extremely wary of being seen as a lame duck with more than three years of his mandate left.
Members of the right and left-wing opposition last week joined forces to vote down the draft without even debating the measures. The government does not have a majority in parliament following 2022 elections.
The government has over the past year frequently used constitutional powers to pass legislation without a vote as it did with contested pension reforms.
But this could also spark a confidence motion that it could lose.
"The political crisis around the immigration bill is a moment of truth where all the fragilities of Emmanuel Macron's mandate are coming together," Le Monde daily newspaper said in an editorial.
Dozens of NGOs hit out at what they described as potentially the "most regressive" immigration law in decades.
It spells bad news "for the rights and living conditions of foreigners, including those who have long been in France", about 50 groups, including the French Human Rights League, said in a joint statement.
A key element is now that social-security benefits for foreigners be conditional on five years of presence in France or 30 months for those who work.
Migration quotas can now be agreed on and there are also measures for dual-citizen convicts being stripped of French nationality.
"With this text directly inspired by RN pamphlets against immigration, we are facing a shift in the history of the republic and its fundamental values," said French Communist Party leader Fabien Roussel.
France's immigrant population is estimated at 5.1 million, or 7.6 per cent of the population.
Authorities believe there are between 600,000 to 700,000 undocumented immigrants in the country.
