Mexico City ? Mexico City lawmakers voted to legalize first-trimester abortions Tuesday, a decision likely to influence policies and health practices across Mexico and other parts of heavily Roman Catholic Latin America.

Abortion rights activists dressed as a Roman Catholic nun and clergyman celebrate Tuesday outside the City Legislature in Mexico City. Mexico City lawmakers voted 46-19 to legalize abortion in the first 12 weeks of pregnancy. Opponents have vowed to challenge the new law before the Supreme Court.

The proposal, approved 46-19, with one abstention, will take effect with the expected signing by the city’s leftist mayor. Abortion opponents have already vowed to appeal the law to the Supreme Court, a move likely to extend the bitter and emotional debate in this predominantly Catholic nation.

“Decriminalizing abortion is a historic triumph, a triumph of the left,” said city legislator Jorge Diaz Cuervo, a leftist social democrat who voted for the bill. “Today, there is a new atmosphere in this city. It is the atmosphere of freedom.”

Nationally, Mexico allows abortion only in cases of rape, severe birth defects or if the woman’s life is at risk. Doctors sometimes refuse to perform the procedure even under those circumstances.

The new law will require city hospitals to provide the procedure in the first trimester and opens the way for private abortion clinics. Girls under 18 would have to get their parents’ consent.

The procedure will be almost free for poor or insured city residents, but is unlikely to attract patients from the United States, where later-term abortion is legal in many states. Under the Mexico City law, women having an abortion after 12 weeks face punishment of three to six months in jail. Those performing abortions after that period would face one to three years in jail.

Mexico City is dominated by the leftist Democratic Revolution Party, at odds with President Felipe Calderon’s conservative National Action Party, which opposed the abortion measure.

“We go to great lengths to protect (sea) turtle eggs,” said city lawmaker Paula Soto, a member of Calderon’s party. “Lucky turtles! It appears they have more people willing to defend them than some unborn children.”

The law alarmed Calderon’s party and prompted authorities to send ranks of riot police to separate chanting throngs of opposing demonstrators outside the city legislature.

A crowd of abortion-rights supporters chanting “Yes, we did it!” gathered at a monument to 19th-century anti-clerical reformer Benito Juarez in downtown Mexico City after the vote.

“I feel happy, because this is a step forward, not backward, for a woman’s right and freedom to choose … about her body and her life,” said demonstrator Gabriela Cruz, 36.

The Roman Catholic church has protested the measure and Mexico City Cardinal Norberto Rivera led a march through the capital last month in opposition. The Archdiocese said Tuesday that it would “evaluate the moral consequences of the reforms” and said Rivera would have no public comment on the vote until Sunday.

The only countries in Latin America and the Caribbean with legalized abortion for all women are Cuba and Guyana. Most others allow it only in cases of rape or when the woman’s life is at risk. Nicaragua, El Salvador and Chile ban it completely.