Upholding a challenge by the national government against the move, which renewed France’s intense debate on Islam, the Council of State said that “very selective exception to the rules to satisfy religious demands… risks affecting the proper functioning of public services and equal treatment of their users”.

The all-in-one swimsuit, used by some Muslim women to cover their bodies and hair while bathing, is a controversial issue in France where critics see it as a symbol of creeping Islamisation.

Led by Green party mayor Eric Piolle, the city of Grenoble in May changed its swimming pool rules to allow all types of bathing suits, not just traditional swimming costumes for women and trunks for men, which were mandated before. Women were also permitted to swim topless.

“All we want is for women and men to be able to dress how they want,” Piolle said at the time.

Tuesday’s court decision – which concerned only the burkini and not the topless ruling or the rules on men’s swim shorts –  was “a victory for the law against separatism, for secularism and beyond that, for the whole republic,” Interior Minister Gérald Darmanin wrote on Twitter, referring to a law introduced last year to counter Islamist radicalism.

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Attempts by several local mayors in the south of France to ban the burkini on Mediterranean beaches in the summer of 2016 kicked off the first firestorm around the bathing suit.

The restrictions were eventually overturned for being discriminatory.

Burkinis are banned in French state-run pools for hygiene reasons — not on religious grounds — while swimmers are not under any legal obligation to hide their religion while bathing.

Grenoble is not the first French city to change its rules.

The northwestern city of Rennes quietly updated its pool code in 2019 to allow burkinis and other types of swimwear.