Archbishop Eamon Martin has said that Stormont has excluded pro-life arguments in its consultation on abortion law changes.
Northern Ireland's Justice Minister David Ford has recommended that abortions should be allowed where the foetus has a lethal abnormality,
The department has begun a public consultation on amending the criminal law on abortion.
Archbishop Eamon Martin said: "I want to bring to your attention a consultation document which proposes that totally innocent and terminally ill babies in the womb will no longer have an absolute right to life, nor the right to all the care and medical support that we would expect and wish for any child or adult who is terminally ill."
He continued: "A delegation from the Catholic Church will be making a robust and unapologetic defence of the right to life of both mothers and their terminally ill children during pregnancy and calling for all the love and support that we as a society can give them."
He said this must include the ready availability of good quality before and after birth hospice care and counselling for those facing the trauma of having a terminally ill unborn child.
"With the support of my fellow bishops, I encourage all those who support a culture of life to respond this week to the consultation process of the Department of Justice and to ask their politicians where they stand on these issues." he added.
Members of the public have been asked for opinions on possible changes to the law in cases of lethal foetal abnormality and rape.
Currently, neither circumstance allows a legal abortion in Northern Ireland.
Lethal foetal abnormality means a baby in the womb has a condition which means it will die while either in the womb or shortly after birth.
Mr Ford said he was making a strong recommendation for legislation to allow an abortion in circumstances where there is no prospect of the foetus being delivered and having a viable life.
Last month the Archbishop of Armagh said there was no absolute obligation to prolong life in all circumstances.
