The Archbishop of Dublin has said that the teaching of the Catholic Church could be used "in a homophobic way".
Dr Diarmuid Martin told RTE that the Church had to be very careful that this was not done in the forthcoming debate on the same-sex referendum in the Republic.
Archbishop Martin said he felt that the debate had already got off to a bad start.
Discussions have to be carried out in a "mature" way so that people can freely express their views, while at the same time being respectful and not causing offence, he said.
He said Church teaching was that marriage was between a man and a woman, exclusively, but that this approach did not exclude gay people from celebrating their union by a different means.
The Irish government has agreed to hold a referendum on civil marriage for same-sex couples in the first half of 2015.
Last April, a Constitutional Convention voted overwhelmingly to recommend that the constitution be changed to allow for civil marriage for same-sex couples.