In a joint statement, Ireland's bishops, archbishops and lone cardinal described the bill, unveiled this week after decades of debate, as "a dramatic and morally unacceptable change to Irish law."
They argued it would be most grievously wrong to give any woman an abortion to assuage her threats to commit suicide, as the bill allows.
"It is a tragic moment for Irish society when we regard the deliberate destruction of a completely innocent person as an acceptable response to the threat of the preventable death of another person," the bishops wrote.
The intervention of Ireland's dominant church in the abortion debate raises the political temperature at a moment when the 2-year-old government of Prime Minister Enda Kenny is already fraying over the merits of the bill.
The government has been under international pressure to clarify the rights of doctors to perform life-saving abortions since October, when a miscarrying Indian woman died from blood poisoning in an Irish hospital after being denied a termination.
If passed, the bill would permit a single doctor to authorize an abortion if the woman's life was in immediate danger from continued pregnancy; two doctors if the pregnancy posed a potentially lethal risk, such as by triggering the return of cancer in remission; and three doctors if the woman was threatening to kill herself.
