(Thousands of gay marriage opponents wave pink, blue and white flags as they take part in the “Manif pour Tous” (Demonstration for All) protest march against France’s planned legalisation of same-sex marriage near the Invalides in Paris, April 21, 2013. REUTERS/Jacky Naegelen)

Thousands of gay marriage opponents waving pink and blue flags marched through Paris on Sunday in a last-ditch protest before a law allowing same-sex union and adoption is passed on Tuesday.

Chanting “We don’t want your law, Hollande!”, some 50,000 protesters massed behind a banner reading: “All born of a Mum and a Dad” and said it was undemocratic to bring about such a fundamental social change without holding a referendum.

Hastily organized after the law’s passage was sped up to circumvent a big rally set for late April, Sunday’s march capped months of protests by a dogged opposition movement that has sullied President Francois Hollande’s flagship social reform.

“We warned the president back in November that we would not give up and that we would do everything to stop this law being passed, or to get it repealed if it is adopted,” one of the protest organizers, Alberic Dumon, told Reuters.