Moroccan-born Faiza Mabchour speaks French fluently, has three children born in France, and a French husband. Yet France's top administrative court last month denied her bid for citizenship.

The reason? Ms. Mabchour wears a burqa, a long veil that some Muslim women use to cover themselves from head to toe. In an interview with officials, she said she wore the burqa not for any special religious belief but because her husband asked her to. A government report stated that "she lives in total submission to the men of her family, and the notion of questioning this submission does not even occur to her."

The court said such a radical religious practice is incompatible with fundamental French values such as the equality of the sexes; thus, she was judged unable to assimilate – a must for citizenship.

The decision raises troubling issues for an ethnically diverse and religiously free society. The court was not denying her French nationality on the basis of her beliefs. Both France's 1789 Declaration of the Rights of Man, as well as the European Convention on Human Rights, guarantee absolute freedom of belief. The court must have denied nationality on the basis of her acts, but her only overt act was the wearing of the burqa.

Yet no French law regulates what clothes people can wear in their homes or general public. (France bans head scarves and other conspicuous religious symbols in public schools.) So Mabchour's burqa is lawful. That France should deny her citizenship on the sole basis of her behavior within the sphere of her own family is inconsistent with normal French tolerance of the private lives of its citizens.

France has by and large adopted the principle espoused in John Stuart Mill's famous 1859 essay On Liberty: "The sole end for which mankind are warranted, individually or collectively, in interfering with the liberty of action of any of their number, is self-protection.... His own good, either physical or moral, is not a sufficient warrant."

In denying Mabchour citizenship when she met all of the requirements save the inherently nebulous one of assimilation, the court came too close for comfort to a demand for religious orthodoxy. It is a paradoxical demand in a nation that insists on the exclusion of religion from the public sphere.

Her case raises two fundamental questions: What is gender equality, and what is citizenship? Is gender equality something more than a guarantee that male and female shall get equal pay for the same work and equal access to opportunities in all spheres to the extent possible? Did the French Supreme Court conclude that the principle of gender equality was violated since she wore the burqa because her husband asked her to? If she had explained that she wore it because that was her own independent choice would the court have given her French citizenship?

Is citizenship like membership in a club where all members must wear coats and ties or like a gang where members must sport a tattoo? Nationality, of course, is a method for defining outsiders. Most states define insiders by birth or parentage. As a leading textbook on immigration and citizenship observes, "Birth is an unambiguous event about which states maintain relatively clear administrative records."

This distinction leads to a supreme irony. As one Internet commentator noted, "you have to be French to wear a burqa." For if Mabchour had been born in Paris, she could wear whatever she pleased, including a burqa, but because she was born in Morocco her burqa rose up as an insurmountable obstacle to her acquiring French nationality.

One cannot help but wonder if Faiza Mabchour had been named Haruko Tanaka and appeared before the commissaire in a silk kimono walking five paces behind her French husband, whether the French court would have reached the same result.

Ronald P. Sokol is a practicing lawyer in Aix-en-Provence, France. He formerly taught at the University of Virginia Law School.