The Broadcasting Authority of Ireland has upheld a complaint against The Mooney Show on RTÉ Radio One.
The show aired on 20 January and featured a discussion on same-sex marriage.
The complainant said both guests and the presenter made statements supporting same-sex marriage.
Dónal O'Latchford-Sullivan of the Family and Media Association said there were no voices opposing same-sex marriage and the discussion amounted, in his opinion, to a debate where one side was forcibly absent.
RTÉ said the item came after release of figures for the number of civil partnerships that had taken place in the year since legislation was introduced.
It said one of the guests, Michael Murphy, was in studio to tell his story as one of the first people in Ireland to "tie the knot" and the other guest, Tiernan Brady from GLEN, was there to give a wider perspective.
The broadcaster also said the item was not a debate on the topic of same-sex marriage and not presented as such, but rather a discussion of the experience of civil partnership.
However, the BAI found that while the same-sex marriage referendum campaign was not under way, "the requirements in respect of fairness, objectivity and impartiality in news and current affairs had not been met".
The BAI considered 12 other complaints at its meeting in June.
One complaint was upheld in part and 11 complaints were rejected.
Two other complaints were resolved by the Executive Complaints Forum.
Upheld by the BAI Compliance Committee
RTÉ Radio One: Mooney: 20 January 2014
Upheld in Part by BAI Compliance Committee
TV3: A Search for Justice: Death in Bray: 10 March 2014
Rejected by BAI Compliance Committee
Today FM: The Last Word: 19 February 2014
TV3: 24 Hours to Kill: 3 February 2014
TV3: Tonight with Vincent Browne: 28 January 2014
TV3: Tonight with Vincent Browne: 30 January 2014
TV3: 5.30 News: 28 February 2014
RTÉ Radio 1: Today with Seán O'Rourke: 3 April 2014
RTÉ Two: The Centre: 24 March 2014 (Four complaints received)
Classic Hits 4FM: The Late Show with Niall Boylan: 30 April 2014
Resolved by the Executive Complaints Forum
RTÉ Radio One: Drivetime: 20 December 2013
RTÉ Radio 1: Fáilte Isteach: 8 February 2014