Mexico City lawmakers are set to defy the Pope and legalise abortion in the capital of the world's second-largest Roman Catholic country today.
Leftist lawmakers dominate Mexico City's local assembly and will vote on allowing women in the capital to abort in the first three months of pregnancy.
Riot police stood between rival groups of demonstrators outside the assembly building as the debate began. Weeping anti-abortion protesters played tape recordings of babies crying and carried tiny white coffins.
In Latin America, only Cuba, Guyana and US commonwealth Puerto Rico allow abortion on demand. Mexico and many other countries permit it in special cases, including after rape, if the fetus has defects or if the mother's life is at risk.
The abortion vote has split Mexico and inspired a letter from Pope Benedict urging Mexican bishops to oppose it.
Church leaders have threatened to excommunicate deputies from the Party of the Democratic Revolution who vote in favour of lifting the ban, which will remain in force in the rest of Mexico.
"They will get the penalty of excommunication. That is not revenge, it is just what happens in the case of serious sins," said Felipe Aguirre Franco, the archbishop of Acapulco.
City deputies from President Felipe Calderon's conservative National Action Party, or Pan, tried to delay the vote until early tomorrow morning.
Leftists, who hold more than half of the assembly's 66 seats, threw out a Pan motion aimed at derailing the abortion bill.
Opinion polls show Mexico's population of 107 million, of whom some 90 per cent are Catholic, is split over the issue.
Supporters of abortion, who are well-represented in the liberal-minded capital, say 2,000 women die each year in Mexico, often poor women who have to resort to unhygienic back-street clinics.
"Yes to abortion, no to hypocrisy," read a poster held by Teresa Rivera, 57, who said she had a clandestine abortion when younger and was dumped in the street by the abortionist. "Excommunicate me," said another banner held by a woman in her 20s.
"There are children dying of hunger, that is a worse sin," said Julia Klug, 54, dressed in a fake cardinal's outfit.
Mexico City lawmakers have recently stirred up controversy by allowing gay civil unions and considering a euthanasia law. Further alarming the anti-abortion camp, Mexican lawmakers have filed a proposal in Congress for a national abortion law.