The Senate has began debating the historic government-backed bill on whether to legalise abortion in Argentiona, with the vote expected to be razor-thin.
Approval would put Argentina, a country where the Catholic Church has long held sway, among only a small group of Latin American nations that have taken similar action.
The highly-anticipated session was opened by Senate President Cristina Fernández de Kirchner, who heads the upper house in her role as vice-president.
Fernández de Kirchner, a former two-term president, said there were 67 of the 72 senators present when the session opened at around 4pm local time, either in person or by video link.
Some 58 people are registered to speak during the debate and the vote is not expected until deep into the night. Most local outlets estimate the vote will take place at around 4am Wednesday morning.
The debate will close with two speakers from each of the main coalitions: for Juntos el Cambio, Tucumán's Silvia Elías de Pérez (strongly opposed) will be followed by the bloc's head in the upper house, Formosa Senator Luis Naidenoff (in favour); Frente de Todos will put up Anabel Fernández Sagasti of Mendoza (pro-reform) followed by Formosa Senator José Mayans.
The bill was proposed by President Alberto Fernández and passed the lower house Chamber of Deputies on December 11, despite fierce opposition from the Church and evangelical Christians.
"I'm Catholic but I have to legislate for everyone. Every year around 38,000 women are taken to hospital due to [clandestine] abortions and since the restoration of democracy (in 1983) more than 3,000 have died of this," said Fernández.
The Health Ministry says there are between 370,000 and 520,000 illegal abortions a year in Argentina.
A similar bill two years ago also passed the lower house but then floundered in the Senate by 38 votes to 31.
This bill aims to legalise voluntary abortions at up to 14 weeks and allows for conscientious objection, though those who oppose the procedure are obliged to quickly refer those seeking abortions to other healthcare professionals. Terminations are currently only allowed in two cases: rape and danger to the mother's life.
According to reports – in a bid to secure the vote of government-aligned Senator for Río Nego, Alberto Weretilneck – the governing coalition has agreed to a minor modification to the bill to ensure its passage. It will see the word "integral" removed from a section referring to potential abortions in the case of the woman's health being at risk.
Despite measures to prevent the spread of the coronavirus pandemic, both pro- and anti-abortion supporters are demonstrating in front of Congress. The rallies are expected to grow increasingly larger throughout the day and into the evening.
Pope Francis wrote a message on Twitter that, while not explicitly mentioning the vote, was interpreted by many as encouraging the senators to vote against the bill.
"The Son of God was born discarded to tell us that every person discarded is a child of God. He came into the world as a child does, weak and fragile, so that we can embrace our weaknesses with tenderness," wrote the Argentine pontiff.
Religious leaders from the Catholic Church and Christian Alliance of Evangelical Churches have called for their supporters "to unite to implore for respect and care for unborn life."
The vote is expected to be razor-thin, despite the governing Frente de Todos coalition holding 41 of the 72 Senate seats.
Not everyone in that alliance supports the bill, while the opposition Juntos por el Cambio coalition is mostly opposed to it.
"In the Senate there are many votes that haven't yet been decided. They will only be known at the end," said Senator Nancy González (Frente de Todos-Chubut)
Should the vote result in a tie, the deciding vote would fall to Fernández de Kirchner, who two years ago changed her stance from anti-abortion to pro-choice.
"This is the moment to finally approve the [abortion] law. Enough of the strategy of criminalisation, stigmatisation and curtailment of freedoms historically inflicted on pregnant women," Fabiola Heredia, the director of the Anthropological Museum at the University of Córdoba, wrote on social media.
Pro-choice activists have campaigned for years to change the abortion laws that date from 1921, adopting a green scarf as their symbol.
"We're going to be in the streets because we're going to have a party. But the Senate is impervious to the street, the decision will be made on the other side" of the congressional walls, said María Florencia Alcaraz, who has written a book about the fight to legalise abortion in Argentina.
'Extremely sensitive issue'
Such changes have always been slow in Argentina: divorce was legalized only in 1987, sex education introduced in 2006, gay marriage approved in 2010 and a gender identity law passed in 2012.
The Catholic Church is fighting this issue all the way. On Saturday, Archbishop Oscar Ojea prayed to the Virgin Mary at the Luján Basilica in Buenos Aires for help in preventing the law from passing.
"Blessed Virgin, pause your gaze on our legislators who must decide on an extremely sensitive issue, so that they may reflect with their minds and hearts," said Ojea at the mass.
In Latin America, abortion is only legal in Cuba, Uruguay and Guyana, as well as Mexico City. In El Salvador, Honduras and Nicaragua, it is totally banned, and women can be sentenced to jail even for having a miscarriage.