Strongly backed by the Catholic church, a coalition of opponents to the proposed legislation has descended on the French capital to march through the streets and make their voices heard.
One protester explained his reasons for taking part:
"There is no reason for two men to be married or for two women to be married. Civil unions were introduced about 10 years ago. There is no reason to change things."
Another stressed that the parenting issue is more crucial to him: "Where I do have questions is regarding adoption. I wouldn't want children to be lied to over adoption. For me a child should have a father and a mother."
During his presidential election campaign François Hollande pledged to push the legislation through by June and he has parliamentary support for the reforms.