French MPs and senators will resume wrangling over an immigration bill on Tuesday after a last-minute disagreement stymied negotiations that had stretched late into the night, with President Emmanuel Macron's government hoping to salvage a flagship reform.

French authorities have been seeking to push through legislation to harden France's immigration law, but members of the right-wing and left-wing opposition last week joined forces to vote down the draft without even debating the measures.

The centrist government, which does not have a majority in parliament, has been locked in frantic talks with the opposition parties to rescue the proposed legislation.

By Monday afternoon, a key member of Macron's party told AFP on condition of anonymity that an agreement on the text of the bill was "practically a foregone conclusion".

A mixed parliamentary commission consisting of seven upper-house senators and seven lower-house lawmakers met from 5:00 pm local time (1600 GMT) on Monday to hammer out a compromise text, but the meeting was interrupted after just minutes due to policy disagreements, including access to social benefits.

The session resumed after a four-hour suspension and continued until half past midnight, when the negotiations snagged on a disagreement over family allowances.

If there is a compromise on the text, the bill could be put to a vote in both chambers on Tuesday.

The deadlock has been deeply frustrating for Macron, who many see as a potential lame duck if he has to spend the rest of his term without being able to implement his reform agenda.

Observers said that to push through the reform, Macron's government risked granting too many concessions to the far-right, which insists the bill is not tough enough.

- 'Stigmatisation of migrants' -

Advocacy groups have criticised the bill, arguing for better conditions for migrants who power many industries in France.

In a letter published in the Liberation newspaper, more than 380 local and national Green legislators urged members of parliament to drop the bill.

"This immigration bill is part of a dynamic of criminalisation and stigmatisation of migrants, promoted by the right and the centre at the national and European level," the letter said.

Government ministers said a compromise needed to be found to avoid handing victory to the far-right.

The commission debating the bill has incorporated several measures proposed by the right, including immigration quotas stipulated by parliament, fines for illegal residence and preventing undocumented migrants from accessing reduced transportation fares.

The right is also pushing for more controversial restrictions, including making social benefits contingent on five years' residency in the country, or 30 months for those who work.

Several thousand demonstrators marched in France on Monday, calling for "resistance" against a "denial of republican values".

Interior Minister Gerald Darmanin indicated that reaching a compromise with the conservative Republicans, whose cooperation is crucial, was still possible.

"We are closer to an agreement than a disagreement," Darmanin, who has championed the bill, said on French news channel LCI on Monday.

The failure of the bill would be a "magnificent" boost for hard-right figurehead Marine Le Pen of the National Rally (RN), Darmanin added.

"Madame Le Pen doesn't want these solutions, she wants problems," he said.

- 'Victory for RN' -

Solidarity Minister Aurore Berge signalled that concessions might be needed to achieve a result.

"If we don't have a text voted through the National Assembly and the Senate, it will be a victory of just one camp, the National Rally," she said.

Yet even if the parliamentary commission agrees on a compromise text, there is no guarantee it would not again face obstacles in the lower house, the National Assembly.

A parliamentary source estimated at the weekend that around 10 percent of the 251 deputies from the presidential camp could abstain or vote against the bill.

Originally proposed by Macron's centrist government with a mix of steps to expel more undocumented people and improve migrants' integration, the draft law was hardened during its earlier passage through the upper house, which is controlled by the right.

The current version has nonetheless been criticised by both the far-right and the far-left for opposing reasons.

France's immigrant population is estimated at 5.1 million, or 7.6 percent of the population. Authorities believe there are between 600,000 to 700,000 undocumented immigrants in the country.