The French Senate has begun a debate on a bill to legalize marriage and adoption for gay and lesbian couples.

The measure easily cleared the lower house of parliament, the National Assembly, in February and is expected to narrowly pass the Senate. Both chambers are dominated by the ruling Socialist Party and its allies.

Socialists, Greens and Communists mostly support the marriage reform, while the conservative UMP Party leads the opposition.

“This is a law for equality,” Senator Jean-Pierre Michel said. “It is not an attack on the traditional family. The so-called traditional family you hear about in the demonstrations – mom, dad, kid – that's not the reality in France anymore, or in other countries, either.”

The Roman Catholic Church has vociferously objected to the government's plans, sending hundreds of thousands of people into the streets of Paris to protest.

(Related: Tens of thousands join Paris anti-gay marriage rally.)

On Thursday, opponents planned to stage protests outside the Senate.

According to Al Jazeera, about 280 amendments have been introduced for debate, and a vote is not expected until April 12 or 13.

A CSA poll released Thursday showed that a majority (53%) of the French people support marriage equality, while 56 percent are opposed to adoption by gay couples.

If the bill is approved, France would become the 12th and most influential country so far to legalize marriage equality.