The Catholic church has distributed a 16-page document to parishes across Ireland ‘briefing’ against same-sex marriage ahead of next year’s referendum.

The Republic of Ireland, which introduced civil partnerships in 2011, is set to vote next May on extending civil marriage to same-sex couples.

A group launched a ‘Yes Equality’ campaign last month, urging people to register to vote ahead of the referendum.

No overt ‘No’ campaign has launched so far – but the Catholic church mobilised this week to state the bishops’ belief that marriage should be between one man and one woman.

The document, distributed to 1,300 parishes, warns: “By introducing any amendment which presents homosexual partnerships as essentially equivalent to marriage, we would be saying that the permanent union of husband and wife and their generation of new life and their nurturing of it together is no longer to be seen as the foundation of society.”

It also states: “The debate at the core of the call for ‘same sex marriage’ is not about equality.

“A major challenge arises from any proposal which seeks to redefine the meaning and purpose of marriage on which the family is founded, changing the definition of marriage by enabling the relationship of a same-sex couple to also become a marriage.

“To do this would mean that marriage, under civil law, would no longer be the committed gift of a man and a woman in a relationship ‘until death do us part’, in the kind of union which can bear fruit in new human lives.

“Any such proposal is based on the assumption that the institution of marriage on which the family is founded, which has always been recognised as ‘the natural, primary and fundamental unit group of Society’, has nothing unique about it and on the assumption that marriage can be stripped of that social standing without obscuring its irreplaceable social role.

“To promote and protect the unique nature of marriage as the union of one man and one woman is itself a matter of justice. Same sex relationships by their very nature are different to marriage.

“The Constitution of Ireland regards the family ‘as the necessary basis of social order and as indispensable to the welfare of the Nation and the State’.

“Any attempt to change this protection would be a radical change in the meaning of marriage – the ‘foundation stone’ of society – in the document that expresses the foundational values of the Irish State.”

It also states that marriage should be reserved for relationships in which “the generation and upbringing of children is uniquely possible.”

“Children have a natural right to a mother and a father, and this is the best environment for them where possible. It is therefore deserving of special recognition and promotion by the State.”