French Muslims have begun joining a mostly Catholic-led movement against marriage for same-sex couples, widening opposition to the reform that the Socialist-led government is set to write into the law by June. Fifty Muslim activists issued an open letter on Monday urging fellow Muslims to join a major Paris protest against the law on Sunday. That followed a similar appeal last Saturday by the influential Union of French Islamic Organisations (UOIF). Leaders of almost all main faiths in France have spoken out against the law, but not called on their followers to march in Sunday's demonstration to avoid giving the opposition campaign an overly religious tone. President Francois Hollande and his government clashed with the Catholic Church last weekend, telling Catholic schools not to discuss the law with their pupils and urging state education officials to report anti-gay discussions at Catholic schools.