The State Council heard arguments Thursday from the Human Rights League and an anti-Islamophobia group who are seeking to reverse a decision by the southern town of Villeneuve-Loubet to ban the Islamic swimsuit.
The ruling, due at 3pm, is likely to set a precedent for around 30 French towns which have banned the burqini, mostly along the sun-drenched southeast coast.
A court in the Riviera resort of Nice upheld the ban this week.
The burqini bans have triggered a fierce debate about the wearing of the full-body swimsuit, women's rights and the French state's strictly guarded secularism.
President Francois Hollande said Thursday that life in France “supposes that everyone sticks to the rules and that there is neither provocation nor stigmatisation”.
Anger over the issue was further inflamed this week when photographs in the British media showed police surrounding a woman in a headscarf on a Nice beach as she removed a long-sleeved top.
The office of Nice's mayor denied that the woman had been forced to remove clothing, telling AFP she was showing police the swimsuit she was wearing under her top, over a pair of leggings, when the picture was taken.
The police fined her and she left the beach, the officials added.
Prime Minister Manuel Valls on Thursday condemned any “stigmatisation” of Muslims, but maintained that the burqini was “a political sign of religious
“We are not at war with Islam… the French republic is welcoming (to Muslims), we are protecting them against discrimination,” he told BFMTV.
But in a sign of the divisions within the Socialist government on the issue, Education Minister Najat Vallaud-Belkacem said the “proliferation” of burqini bans “was not a welcome development”.
'No link to terrorism'
Vallaud-Belkacem, who is of Moroccan origin, took issue with the wording of the ban in Nice which linked the measure to the jihadist attack in the resort last month in which 86 people were killed.
“In my opinion, there is nothing to prove that there is a link between the terrorism of Daesh and what a woman wears on a beach,” she said, using another term for Islamic State.
But Valls contradicted his minister's claims, saying the bans were necessary to maintain “public order”.
The former president, Nicolas Sarkozy, who this week launched his bid to regain the presidency, has described the burqini as a “provocation”.
The administrative court in Nice ruled Monday that the Villeneuve-Loubet ban was “necessary” to prevent public disorder after the truck attack in Nice and the murder of a Catholic priest by two jihadists in northern France.
The so-called burqini bans never actually mention the word burqini, although they are aimed at the garment which covers the hair but leaves the face visible and stretches down to the ankles.
The vague wording of the prohibitions has caused confusion.
Apart from the incident in the photographs in Nice, a 34-year-old mother of two told AFP on Tuesday she had been fined on the beach in the resort of Cannes wearing leggings, a tunic and a headscarf.
“I was sitting on a beach with my family. I was wearing a classic headscarf. I had no intention of swimming,” said the woman, who gave only her first name, Siam.
London Mayor Sadiq Khan, the first Muslim mayor of a major Western capital, condemned the bans as he visited Paris Thursday.
“I don't think anyone should tell women what they can and can't wear. Full stop,” he told the London Evening Standard newspaper.
France firmly separates religion and public life and was the first European country to ban the wearing of the Islamic face veil in public in 2010.