The European Court of Human Rights has ruled that Muslim parents in Switzerland cannot refuse to send their daughters to mixed school-run swimming lessons.
It was responding to a challenge by a Turkish-Swiss couple who argued the classes violated their beliefs.
The ECHR accepted that the refusal by authorities to exempt girls from the lessons interfered with their freedom of religion.
But the interference, it said, was justified by the need to protect the children from social exclusion.
School plays "a special role in the process of social integration, particularly where children of foreign origin were concerned," ruled the court in Strasbourg.
Swimming lessons are "not just to learn to swim, but above all to take part in that activity with all the other pupils", it added.
The court found that the Basel authorities had tried to accommodate the parents' beliefs by, for instance, allowing the girls to wear the full-body "burkini" swimsuit.
The court also said that the fine of 1,400 Swiss francs (€1,300) imposed on the couple in 2010 after a warning was "proportionate to the aim pursued" of getting them to comply with the regulation.
The case was brought by Aziz Osmanoglu and his partner Sehabat Kocabas, whose daughters were born in 1999 and 2001.
All their appeals were rejected by Swiss courts, after which they took their case to Strasbourg.
Today’s ruling is not final. The couple has three months to appeal the decision.