Trade unions and anti-racism groups have criticised an initiative by the French interior ministry to check on the number of Muslim children who skipped school last month to celebrate Eid al-Fitr.
The festival, which concludes the month of Ramadan, is observed as a holiday in Muslim-majority countries and fell on Friday, April 21, for most believers this year.
France's interior ministry said Sunday that it had ordered "an evaluation of the level of absenteeism recorded on the occasion of Eid al-Fitr".
The ministry "regularly studies the impact of some religious festivals on the workings of public services, and notably in the educational sector", said a statement from junior minister Sonia Backes.
In the city of Toulouse, police asked the heads of local schools to report the number of absent children on April 21, leading to accusations that authorities were creating a registry – which was denied by Backes.
The country's biggest teachers' union, the FSU, said in a statement addressed to Interior Minister Gerald Darmanin on Monday that it "harshly denounces this operation".
"Attempting to create statistics by security forces on religious beliefs and their observance or not, above all in a school environment, goes against the basic principles of secularism and fundamental rights," it said.
The smaller CGT Educ'ation union called it a "scandalous and dangerous stigmatisation".
Using police to carry out the checks was "particularly shocking because it associates the observance of the Islamic religion to an issue of security", the anti-racism group SOS Racisme said.
France has a strict form of secularism that seeks to separate the state and its various branches from religion and religious bodies, while guaranteeing the freedom to worship to all.
Collecting information about ethnicity or religious beliefs is also generally prohibited in France under the country's anti-discrimination laws.
Owing to the country's Catholic heritage, major Christian festivals such as Christmas or Easter are observed as public holidays in France when schools are closed.