Two women wearing Islamic face veils or niqabs were detained by police in Paris Monday on the first day of a ban on Muslim garments that cover the face.
The two women were part of a group of a dozen people protesting the ban - the first of its kind in a Western country - in front of Notre Dame cathedral.
A police spokesman told the German Press Agency dpa that three people had been detained over the protest "because they were taking part in an undeclared demonstration" and not because two of the women were wearing the niqab.
They had been brought to a police station for an identity check, the spokesman said. He could not confirm whether they had been fined.
The demonstration was organized by an organization called Don't Touch My Constitution, which has led opposition to the law that was passed last October but only came into effect Monday.
Under the law a woman wearing a burqa (a garment that covers the body from head to toe) or a niqab (a veil that covers the face with just a slit for the eyes) can be fined 150 euros (217 dollars) or forced to take classes on citizenship.
Around 2,000 women are estimated to be affected by the ban, which includes public parks, restaurants, cinemas and beaches but does not include private homes, places of worship or cars.
Within hours of the ban a woman wearing a niqab boarded a train to Paris from the southern city of Avignon.
Kenza Drider, 32, told reporters she considered the law a violation of her rights as a citizen of France and a European but that if she was cited by police.
"I am committing no crime," said Drider, who was on her way to Paris for a television interview. There were no reports of her being stopped by police.
Proponents of the ban say it aims to protect women from Islamic fundamentalism and improve public security.
The law's detractors argue it will make imprison burqa or niqab wearers in their homes.
Police have been ordered to apply the law with as much tact as possible, and to try to persuade rather than coerce women to show their face for identity checks.