Currently, abortion is only allowed in the European country until the 12th week of pregnancy in cases of rape, a malformed fetus or if the woman's life is in danger. But Sunday’s referendum might change that.
Sunday's referendum will ask voters if they agree with the legalization of abortion, regardless of the circumstances, until the 10th week of pregnancy.
Cardinal Jose da Cruz Policarpo is urging Catholic voters to consider the sanctity of life when casting their votes.
The conscience of Christians regarding abortion "must be illuminated not only by natural light but also by the word of God and the teachings of the Church," said the cardinal in a text published on the Archdiocese of Lisbon website.
Throughout the campaign toward the referendum, Catholic bishops and clergy have been vocally opposed to any changes to the abortion law.
In a 1998 referendum, voters upheld the existing abortion law by 51 percent to 49 percent, but the result was declared void as nearly seven out of 10 voters stayed away.
Portugal's top cleric urged followers to reject abortion as the predominantly Catholic country heads into a weekend referendum on whether to do away with the country's pro-life legislation.