The Constitutional Council said a circular from Interior Minister Manuel Valls saying mayors could not refuse to officiate at the ceremonies "has not infringed their freedom of conscience," Radio France International reported.
The circular was issued in May after passage of a law allowing same-sex marriage. It said refusal to perform a marriage could be punished by a five-year prison term and a $10,200 fine. Mayors also could be suspended or removed from office.
Some mayors have refused to perform same-sex marriages but have not been punished, officials said.
Wisconsin business offering 'therapeutic cuddling' forced to close
Campus cop fatally shoots Texas student during traffic stop