Women in the French city of Grenoble should not be allowed to wear full-body "burkini" swimwear in public pools, a top court has ruled.
The ruling trumps a decision made a month ago by the city's council to allow burkinis.
Body-covering swimwear - which leaves only the face, hands and feet exposed - is often worn by Muslim women who want to preserve their modesty for religious reasons.
But Grenoble's move sparked criticism from conservative and far-right politicians who said it would undermine France's principle of secularism in public life.
The country's government challenged the council's decision and a lower administrative court suspended the measure.
Grenoble then took its case to the country's top administrative court, the Council of State, which upheld the earlier court order.
The Council of State said: "The new rules of procedure for the municipal swimming pools of Grenoble affect… the proper functioning of the public service, and undermines the equal treatment of users, so that the neutrality of public service is compromised."
After the latest ruling, interior minister Gerald Darmanin said Grenoble's act had been "definitively overruled". He called it a "victory for... secularism and above all for the Republic".
Grenoble city council said its main aim had been to guarantee equal treatment for all users.
Clothing rules in public pools in France are strict for hygiene reasons, say authorities. Caps have to be worn, and baggy swimming trunks are generally banned.
No nationwide burkini ban
Supporters of the burkini claim some women would opt, or be pressured by relatives, to stay away from public swimming pools if they were not allowed to wear the body-covering item of clothing.
There is currently no nationwide ban in France, but they are prohibited in many public pools across the country.
Leader of the far-right National Rally party Marine Le Pen, who was runner-up to Emmanuel Macron in April's presidential elections and also did well in last Sunday's parliament elections, has said she wants to bring in a law banning burkinis in municipal pools.
'Bans of burkinis discriminate against Muslim women'
Muslim rights organisations say bans on burkinis restrict fundamental liberties and discriminate against Muslim women.
The UN has called on France to lift the burkini bans that started in 2016, with the spokesman for the UN High Commissioner for Human Rights, Rupert Colville, saying the prohibitions "fuel religious intolerance and the stigmatisation of Muslims".