Opponents to a government-sponsored bill that would legalize marriage and adoption for same-sex couples took the streets of Paris Sunday in the biggest demonstration over a social issue in France in nearly 30 years.

Coming from across the country, protesters held balloons and waved banners and flags that read, “All born from a man and a woman,” and “Our wombs aren’t shopping carts.” They demanded that the bill be withdrawn, arguing that legalizing marriage and adoption for same-sex couples is against nature.

Organizers of the protest said 800,000 to 1 million people attended the demonstration, while police estimated the turnout at 340,000. Demonstrators, including prominent right-wing and far-right opposition politicians, marched through the city before converging on the Champs-de-Mars, where the Eiffel Tower sits.

Frigide Barjot, a Catholic comedian and spokeswoman for the protestors, delivered a speech before the crowd in which she addressed French President François Hollande directly. “You, president of the republic, will you be the one decreeing that one can be born without a man or a woman?” she said.

Mr. Hollande pledged to legalize marriage and adoption for same-sex couples when he ran in last year’s presidential election. On Sunday evening, French Justice Minister Christiane Taubira told TF1, a French television channel, that the bill would go to Parliament despite the protest and that no referendum would be held on the issue.

“It’s just a law that opens new freedom,” Ms. Taubira said. “It’s a protective law for couples and ... most importantly, for children.”

A Jan. 10 survey by pollster BVA Opinion found 58 percent of respondents supported legalization of same-sex marriage while 41 percent opposed it. Among those opposed to same-sex marriage, 58 percent said they would nonetheless attend the weddings of their children if they were gay or lesbian.

However, by at least one measure, public support for adoption by same-sex couples has declined in recent months. A November 2012 BVA Opinion poll showed that 50 percent of respondents supported adoption for same-sex couples, while 47 percent opposed it. But by January 2013, a majority of those surveyed – 53 percent – now said they opposed the measure, with only 43 percent still supporting it.

Alexis Brézet, the editor of the right-leaning Le Figaro newspaper, sided with the protesters in a column on Monday and wrote that just because a majority of voters elected Hollande doesn’t mean a majority of citizens supports the bill. “The elementary wisdom now would be to put the bill on hold and to end ... where we should have started,” Brézet wrote. “A national debate, a real one.”

The left-leaning Libération newspaper called the protest “massive” in its Monday edition but wrote that demonstrators were out of touch with reality “at a time where, in France, more than one out of two children is born out of wedlock, and where 1.2 million children live in stepfamilies.”

Marie-Claude Picardat, the co-president of the Association of Gay and Lesbian Parents and Future Parents, says she is confident the government won’t backpedal on the bill despite Sunday’s protest.

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“What matters to me is to see that the government is very motivated and that the bill will pass as was announced in the platform of the candidate for president of the republic who was elected with millions and millions of vote,” Picardat says, referring to Hollande’s victory in last year’s presidential election.

A demonstration in favor of the bill will be held on Jan. 27, just two days before the discussion of the bill starts in the National Assembly, France’s lower parliamentary chamber. The bill is likely to pass, as Hollande’s Socialist Party and its allies hold a majority of seats in both the National Assembly and the Senate.