Poland has one of the strictest abortion legislations in Europe and the final decision on banning or liberalising it will be taken on Friday.
The Polish parliament started debating draft legislation on banning abortion on Thursday and is set to announce its decision on Friday.
A poll published this week by the Newsweek Polska magazine showed that 74 per cent of Poles want to keep the existing law, which only allows abortion in cases of rape or serious health problems of the baby or the mother.
The country of 38 million people sees less than 2,000 legal abortions a year, but women's groups estimate that another 100,000-150,000 procedures are performed illegally or abroad.
The Catholic Church supports the proposal, introduced by an independent conservative think-tank, but the ruling Law and Justice (PiS) party appears reluctant to give its full backing.
Poland remains one of Europe's most devout Catholic nations, with about 90 per cent of citizens declaring allegiance to the church.
People standing against the abortion law created the hashtag #CzarnyProtest, which means "black protest," calling on people to wear black to show solidarity.
Aside from the abortion ban, the parliament will also debate draft legislation that would limit in-vitro fertilisation (IVF), also called the "test-tube baby" treatment.