Thousands of people rallied in central Dublin on Saturday against the government's plan to allow limited access to abortion where a woman's life is in danger.
Organisers said more than 40,000 massed outside government offices in the capital for the "National Vigil for Life", making it the largest anti-abortion demonstration in Ireland's history.
Ministers have agreed draft legislation to allow for limited access to abortion in cases where a woman's life is at risk, including the threat of suicide, but the proposal has divided the ruling coalition.
"The turnout today shows that the middle ground of Irish opinion is increasingly concerned about the government's abortion legislation," Pro Life Campaign spokeswoman Caroline Simons told a crowd waving colored balloons and placards.
"There are people here who never attended a pro-life event before. The message is getting through that this legislation is not restrictive or about saving women and children's lives."
A two-decade-old debate over how Ireland should deal with a Supreme Court ruling that abortion be permitted when a woman's life was in danger was re-opened last year after the death of a woman who was denied an abortion of her dying foetus.
Successive governments had sidestepped acting on the ruling, the result of a challenge by a 14-year-old rape victim in the so-called "X-case" of 1992 to a constitutional amendment nine years earlier that intended to ban abortion in all instances.
However the death of Savita Halappanavar and subsequent large-scale protests from both sides of the debate spurred ministers into action despite misgivings among some members of Prime Minister Enda Kenny's conservative Fine Gael party.
The influence of the Catholic Church over society has waned since the 1980s and a younger, secular generation wants to end the practice of Irish women travelling to Britain to terminate their pregnancies.
But the issue still polarises opinion.
The government hopes to enact the legislation before parliament adjourns in July and Kenny has said he expects the government to vote as one on the issue, meaning that any defectors could be expelled from his party.
While this would be unlikely to threaten the government's record majority, it would be a blow for Kenny who, midway through a five-year term, has kept all but one of Fine Gael's members of parliament on side, even as he pushes through austerity measures required under an EU/IMF bailout.