The director of Ireland's National Library has refused to comment on reports that the Mormons are using its records to re-baptise dead Catholics in their faith.
However Aongus O hAonghusa, director of the National Library of Ireland, has said that microfilms of Catholic parish registers are already available in many local heritage centres throughout the country.
The controversy has arisen in the Irish Catholic newspaper after it reported that Archbishop Dermot Clifford and Bishop Bill Murphy have written to the National Library stating that they were "taken aback" that records handed over by the Church are now open to "all comers".
This relates to Mormons -- or members of the Church of Jesus Christ and the Latter Day Saints -- trawling through parish records and using the names to posthumously baptise dead Catholics in the Mormon faith as part of a so-called "proxy baptism service".
A spokesperson for the Mormons told the Irish Catholic: "Posthumous baptisms by proxy have been common practice for the Mormons for more than a century allowing the dead to be baptised into the faith so they may be united in the after life", and she added that all available records are used to carry out this practice.
But Mr O hAonghusa, though refusing to be drawn into the controversy, has said that most Irish dioceses now allow unrestricted public access to their records, which have been handed over to the National Library.
"It is worth noting that all bar three Catholic dioceses had lifted any restrictions on access to the National Library's holding of microfilmed parish-registered records some years ago. In the case of the remaining three dioceses, the level of access varied from none in the case of records from the diocese of Cashel and Emily to minor restrictions in the case of the diocese of Cloyne and Kerry.
"You should be aware that microfilms of the Roman Catholic parish registers are already available in many local heritage centres through the country."
The growing concern in the Irish Church has emerged just months after the Vatican warned bishops' conferences around the world about Mormons accessing diocesan and parish registers, according to the Irish Catholic.
A source told the newspaper there is now a fear among senior Irish churchmen that making the records freely available will "encourage Mormons to baptise dead Irish Catholics en masse".
Archbishop Clifford told the Irish Catholic: "The Archdiocese has not surrendered its claim to copyright of the records held in trust at the National Library. In due course, a full statement on the matter will be made."