Boston cardinal Sean O'Malley skipped a college commencement in protest at its decision to honour Taoiseach Enda Kenny, who backs laws to permit abortion.
The cardinal's views were echoed outside the Boston College ceremony on Monday by a few dozen anti-abortion activists.
The protesters gathered at an entrance to the stadium where Mr Kenny gave the commencement address and received an honorary degree, with some holding signs saying it was a scandal that the Catholic school was hosting him.
The bill supported by Mr Kenny allows abortion only if a doctor authorises it to save a woman's life, but opponents say it would lead to widespread abortions because of a provision that permits it if a woman threatens suicide.
Protester CJ Doyle of the Catholic Action League called that "the proverbial Mack truck loophole" and said Boston College's decision to honour Mr Kenny undermined the church's anti-abortion teachings. "What rational person can reasonably be expected to take seriously Catholic opposition to abortion when our own Catholic institutions honour someone who's trying to legalise abortion in his country?" he said.
Mr Kenny did not mention the controversy during his address to the graduating students.
Afterwards he told reporters the bill did nothing to change an 1861 Irish law that makes abortion a crime punishable by life in prison. Instead, it "is setting out clarity and legal certainty, that is intended to save lives, not to end them", he said.
The current bill is being debated following last year's death of a woman who was admitted to hospital at the start of a protracted miscarriage during her 17th week of pregnancy. Doctors refused her request for an abortion and she died of massive organ failure.
The bill permits a single doctor to authorise an abortion if the woman's life is in immediate danger. Two doctors must approve if a pregnancy poses a potentially lethal risk. The approval of three doctors is required if the woman is threatening suicide.
Boston College spokesman Jack Dunn said Mr Kenny's invitation was unrelated to the controversial legislation and was offered solely because of historical ties between his country and a school founded by an Irish Jesuit to serve Irish immigrants. He said the invitation to Mr Kenny in no way eroded the school's anti-abortion stance.