The Republic of Ireland is to hold a referendum on gay marriage in 2015, its Government said earlier this week.
The public vote will come in the same year as a UK general election.
Ireland’s Prime Minister Enda Kenny said he supports gay marriage “very strongly” and that the Government will actively campaign for it.
But the Roman Catholic Church has already said it will seek to keep the law as it is, saying: “To change the nature of marriage would be to undermine it as the fundamental building block of our society.”
Bishop Denis Nulty added that, “married love is a unique form of love between a man and a woman which has a special benefit for the whole of society”.
And the Iona Institute, a campaign group which promotes the place of marriage and religion in society, said changing the law for same-sex couples is not an issue of equality.
Dr John Murray, one of the directors of the organisation, said: “This debate is really about the value we attach to a child having a mother and a father as distinct from two fathers or two mothers.”
“Do we think having the love of a mother and a father confers any special advantage on children or not?”
“Do we think the natural ties between children and their parents matter at all?”
Earlier this year a body which looks into changes to Ireland’s constitution recommended legalising gay marriage.
The vote is expected to be held on the same day as up to six other referendums on issues regarding the Republic’s constitution.
Civil partnerships were introduced in Ireland in 2010.