Lawmakers in Argentina are due to vote on a draft bill that would allow women to have abortions in the first 14 weeks of their pregnancies.
The bill has proven highly divisive and deputies have been split almost evenly in the run-up to the lower house vote, with more than a dozen still undecided.
If approved, the bill will still have to go to the Senate.
Abortion is currently illegal except in cases of rape or when the life or health of the woman is at risk.
Women seeking abortions also have to apply to a judge for permission, which critics say can unnecessarily delay the procedure.
President Mauricio Macri has asked members of the chamber of deputies to vote according to their conscience. Although Mr Macri strongly opposes the bill, he said he would not veto it if it were passed by Congress.
The move comes a year after lawmakers in neighbouring Chile voted in favour of lifting that country's total ban on abortions.
Both supporters and opponents of decriminalising abortion have gathered on opposite sides of the Congress building in Buenos Aires in an effort to sway undecided lawmakers.
The momentum in favour of a change in the law has grown over the past months and was further boosted by the overwhelming vote for overturning the abortion ban in Ireland.
There have been huge marches backing the bill led by #NiUnaMenos (#NotOneLess), a movement first created to fight violence against women but which has since expanded across much of Latin America to stand up for women's rights.
Tens of thousands of people have shown their support by wearing green handkerchiefs but there has also been stiff opposition led by the Catholic Church.
One of the politicians leading the "no" vote is Vice-President Gabriela Michetti. She argues that "being in favour of life is much more progressive and respectful". "If a woman does not want to be a mother, whatever the motive, she can entrust the child for adoption," she said.
Non-governmental organisations say an estimated 500,000 abortions a year are carried out clandestinely, often in conditions which pose a health risk for women and girls.
In most of Latin America there are tight restrictions on abortions and in some countries such as the Dominican Republic, El Salvador and Honduras there is a total ban.
If Argentina were to pass the bill it would be the most populous nation in the region to lift restrictions on abortions.