Bishops in the Catholic Church of Ireland have attacked a civil partnerships bill for “undermining” marriage.

At a press conference last week, the Bishop of Dromore, John McAreavey, the Bishop of Elphin, Christopher Jones and the Bishop of Ferns, Denis Brennan, claimed that people who refused to carry out the ceremonies for gay couples would face fines and “up to six months in prison”.

The bill is currently passing through Ireland’s parliament. It will grant rights related to domestic violence, residential tenancies, succession, refugee law, pensions and immigration.

However, it will not give legal support to children being brought up by gay couples and will not allow a non-biological parent to adopt their own children.

The Irish Times reports that the three bishops released a statement titled Marriage Matters, which said that gay relationships could never be equal to straight ones.

It said: “A same-sex couple cannot be husband and wife. A same-sex couple cannot procreate a child through the sexual act which expresses married love.

“Same-sex relationships, by their very nature, cannot be considered equal to marriage or almost equal to marriage.

“[The bill] ignores the unique and proper place of husbands and wives, the place of mothers and fathers, and especially the rights of children, who deserve from society a clear understanding of marriage as they grow to sexual maturity.”

They added that the bill “represents a fundamental revolution in our understanding of marriage and the family and cannot go unchallenged”.

Bishop Jones told Thursday’s press conference he was “very worried” about the bill and that he and other bishops were considering whether to take Constitutional action should it become law.

He said: “We are really very concerned that the Civil Partnership Bill is going to undermine marriage by conferring all the rights on same-sex unions as marriage, equating same-sex union to marriage itself.”

Justice minister Dermot Ahern refused calls from religious leaders to include a faith “opt-out” for registrars to refuse to carry out the ceremonies.

The bishops claimed that anyone “who conscientiously refuses to carry out such a [civil partnership] ceremony will face a fine and up to six months in prison”.

They added: “Christians, Jews and Muslims or anyone else who refuses to make halls and other facilities available for a celebration or reception connected with a same-sex partnership will face prosecution and fines.”

The bill was presented to parliament in December and completed its second stage in the Dail in January. It will now go to a committee for further scrutiny.

Gay rights campaigners have welcomed the “speedy” progress of the legislation, but continue to cite concerns that it does not recognise children of gay parents.