The Bishop of Ossory, Dr Dermot Farrell, has suggested abortion is sometimes far worse than rape.
Bishop Farrell has claimed that once introduced, abortion would be extremely difficult to restrict.
His warning came in a letter which was available in the diocese.
But Bishop Farrell told Pat Kenny that while it was available at every mass, it may not have been read at every mass.
"It was available in the church... some priests may have read excerpts of it, others may have published part of it.
"It's unlikely any of them would have read the entire thing in its completeness".
"What we're voting for on the 25th of May is to end the life of a child without restriction up to 12 weeks, and for unspecified health reasons then up to 24 weeks.
"My fundamental argument is that the right to life is fundamental - and that all other rights are based on that, no matter what other right we talk about".
On the issue of abortion in cases of rape, he said: "First of all rape is a violent act and it's a violent crime against a woman - a terrible crime.
"And sometimes, what I understand from women who have been raped, is that the abortion that followed sometimes after rape was far worse than the rape itself".
He claimed the issue of abortion is "the most important social and justice issue of our time.
"It's going to shape the kind of Ireland that we have.
"What we're voting on here is not just a law, but a value system".
He was appointed by Pope Francis on January 3rd this year.