If passed, the bill would make Argentina the first big country in predominantly Catholic Latin America to allow abortion on demand.
Argentina was on the cusp of legalizing abortion over the objections of its influential Roman Catholic Church, with the senate preparing to vote on a measure that has the backing of the ruling party and has already passed in the lower house.
The vote is expected to be close after what is likely to be a marathon debate, beginning at 4 pm (1900 GMT).
“For decades we have been waiting for this moment,” said more than 1,500 prominent Argentine personalities in an open letter to senators.
“This is a time to make history. The world is watching.”
On the other side of the debate is the Catholic Church, which is calling on senators to reject the proposal to allow women to end pregnancies up to the 14th week. Argentina is the birthplace of Pope Francis.
Argentine law now allows abortion only when there is a serious risk to the health of the mother or in cases of rape.
Feminist groups and other advocates of the bill called for people to demonstrate at provincial capitals around the country on Tuesday while the measure is debated in the Senate. Demonstrations by people against the bill are also expected.
Legal abortion is extremely rare in Latin America because of the long history of opposition by the Church. Across the region, abortions are available on demand only in Communist Cuba, comparatively tiny Uruguay, and some parts of Mexico.
The change in law has been rejected by Argentina’s Congress before, but this is the first time that such a bill is being presented to lawmakers with support from the ruling government. In 2018, before President Alberto Fernandez was elected, a similar bill was rejected by a slim margin.
The measure is accompanied by side legislation aimed at assisting women who want to continue their pregnancies and face severe economic or social difficulties.