France is facing a fresh backlash against its strict secular policy after it emerged a 15-year-old Muslim girl was sent home from school because she was wearing a long black skirt.
The student, named as Sarah, was twice blocked from classes because the principal said her skirt broke a ban on religious signs in schools.
The girl removed her headscarf but said the skirt was not a religious symbol.
The case has provoked angry reactions online.
The hashtag #JePorteMaJupeCommeJeVeux, or "I wear my skirt how I want to" has had more than 45,000 tweets since Tuesday.
The schoolgirl was sent home in Charleville-Mezieres in the northern Champagne-Ardenne region twice in April, according to reports.
Nicolas Cadene, an official advising the prime minister on secular issues, has said that wearing a long black skirt to school does not break the rules.
A ban on Muslim headscarves and other "conspicuous" religious symbols at state schools was introduced in 2004, and widely welcomed in a country where the separation of state and religion is enshrined in law.
"The 2004 law says that symbols and clothing worn to show religious affiliation are prohibited," Mr Cadene told Buzzfeed France (in French).
"We obviously think of the veil, the kippah, a large cross, a Sikh turban... A black skirt do not contravene the law."
But critics say some schools are increasingly imposing extreme interpretations of the ban.
Eight Muslim students were told to change by their school in Montpellier when they arrived in long skirts last month, local media say.