Story highlights A proposed bill would give same-sex couples new marriage and adoption rights

French President Francois Hollande pledged new legislation while campaigning

His plan faces stiff opposition from the Roman Catholic Church and social conservatives

Hundreds of thousands of protesters took to the streets of Paris on Sunday decrying the French president's plan to legalize same-sex marriage and adoptions.

They converged near the Eiffel Tower, chanting and waving flags, posters and balloons.

"I do not personally agree with gay marriage as I am a Christian and believe what the Bible says about marriage being between one woman and one man for a life time," said CNN iReporter Oluwasegun Olowu-Davies, who shot video of the march with his phone.

"If your lifestyle doesn't allow you to conceive, there is a reason," he said.

Extending the right to marry and adopt to same-sex couples was one of President Francois Hollande's electoral pledges in campaigning last year.

After his win, the Cabinet approved a draft bill that is expected to go before the National Assembly and Senate soon. It is likely to be voted on in February or March. If passed, it would mark the biggest step forward for French gay rights advocates in more than a decade.

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The plan faces stiff opposition from the Roman Catholic Church and social conservatives.

Cardinal Andre Vingt-Trois, the archbishop of Paris, voiced his opposition at a meeting of French bishops in Lourdes last year.

Opening up marriage to same-sex couples "would be a transformation of marriage that would affect everyone," he said.

At the same time, failing to recognize gender difference within marriage and the family would be a "deceit" that would rock the foundations of society and lead to discrimination between children, he said.

Other religious groups in France, including Muslims, Jews and Buddhists, have also expressed their concern over the draft bill, and more than 100 lawmakers are against the legislation, according to CNN affiliate BFMTV.

Hundreds of mayors around the country have also voiced their opposition, which has won wide backing from gay rights advocates.

The French gay, lesbian and transgender rights group Inter-LGBT said the law, if passed, "would be a major advance for our country in terms of equality of rights."

Lawmakers have a "unique opportunity" to put an end to outdated discrimination, the group said in a statement. "The law must allow all couples to unite themselves as they wish and must protect all families, without discrimination on the grounds of sexual orientation or gender identity," it said.

A law legalizing civil unions was introduced in 1999 in France under a previous Socialist government.

Known in France as the PACS (pacte civil de solidarite), the civil union agreement can be entered into by gay or straight couples and confers many but not all of the rights of marriage.