On Sunday, tens of thousands of people took to the streets to demonstrate against President Emmanuel Macron’s legislation, which the National Assembly passed last month by 349 votes to 186.

Critics say it bears all the hallmarks of the far-right.

Despite the bill’s hefty margin of success, 27 members of Macron’s governing coalition voted against the bill – and another 32 abstained.

In the wake of the vote, French Health Minister Aurelien Rousseau quit in protest.

What’s in the new immigration bill?

The new bill includes amendments on residency and citizenship – and implements a raft of measures aimed at taking a tougher line on immigration.

These include provisions that would make it harder for people in France to bring over family members, and see welfare benefits tougher to access.

Children born in France to foreign parents would, according to the new bill, no longer become automatic French citizens under its jus soli – or “right of the soil” – policy and would instead have to apply for citizenship between the ages of 16 and 18.

Critics of the bill have accused Macron of giving succour to the hard right.

Far-right politician Marine Le Pen, who ran for the presidency in 2012, 2017 and 2022, hailed the legislation after it was passed in December.

“One can rejoice in an ideological victory … national preference is now inscribed in law, meaning the French will have an advantage over foreigners in accessing certain social benefits,” said Le Pen, who is the daughter of Jean-Marie Le Pen, the former president of the far-right French National Front.

Is the immigration bill just a battle between left and right?

While the immigration bill has angered the left in French society, this issue shouldn’t be seen as a strictly left versus right debate says Philippe Marliere, a professor in French and European Politics at University College London.

“One of the reasons for this is that the bill seems to undermine underlining [established French] constitutional principles,” he told Al Jazeera

Indeed, “national preference” – the French first doctrine name-checked by Le Pen and long espoused by the French far-right – had “up until now [been] rejected by the rest of the political spectrum”, but, by virtue of this legislation, has today made it into the political mainstream.

“[National preference] has been [promoted] by the far-right in France for 50 years and with this bill it has got what it has always wanted,” said Marliere of the principle which, say its detractors, would codify a two-tier system in France by prioritising French citizens over legal migrants.

“But without even winning a general election and [Marine] Le Pen being elected president.”

Yet, the bill’s biggest test, said Marliere, comes on Thursday with the judgement of the Constitutional Council.

What is the Constitutional Council?

The Constitution of the Fifth Republic, which was designed by French World War II hero, Charles de Gaulle, came into being on October 4, 1958. The Constitutional Council, the highest constitutional authority in the land, was established at the same time.

The nine-member council customarily examines new laws to ensure they are in keeping with the tenets of the French constitution.

Last April, for example, the council ratified plans by Macron to raise the French retirement age from 62 to 64. But, just like his immigration bill, Macron’s legislation on pension reform sparked popular protest, even after the decision of the Constitutional Council to approve the bill.

However, the decision of the council meant that Macron could sign his bill into law.

Will the Constitutional Council approve Macron’s immigration bill?

“People expect the Constitutional Council to deem some of the provisions in this controversial immigration bill as anti-constitutional,” said Marliere.

He added it is likely that “parts of the legislation will prevail and will stay” but if, as expected, the council decrees certain aspects of the bill unconstitutional, then the French government will have two options.

It can either accept the decision of the council and enact the law as it stands or it can take the bill back to parliament and rewrite the provisions the council judges as constitutionally defective.

Macron, who has denied that his legislation echoes that of the far-right, has stated that the bill is “what the French wanted”.

But with the president himself even admitting to some shortcomings in the bill – he called it the “fruit of a compromise” in December – the council judgement promises much in the way of political drama.

“Macron will be hoping, as we speak, that the council will not be too harsh in its assessment,” explained Marliere. “That any censorship of the law will not be too substantial.”

He added that any council decision which censored large parts of Macron’s legislation would be seen as “a complete political defeat” for the president.