A letter to young people from Roman Catholic bishops condemning gay marriage has been rejected by other Christian leaders.
The letter to "Kiwis of Generation Y" from all six of New Zealand's Catholic bishops advises against allowing same-sex couples to marry in the eyes of the law for the sake of "society as a whole".
"This is no small matter, nor quibbling about words; this is an attempt to re-engineer the status and structure of family life in New Zealand," they wrote.
Fifty clergy and laity from Anglican, Presbyterian, Methodist and Quaker denominations lashed out at the bishops and called on them to reconsider their position on the Marriage Amendment Bill.
"We think it's time the Church recognises and encourages those in same-gender relationships who wish to pledge their love and fidelity to each other in the rite of marriage," the group wrote back to the bishops.
"To suggest, as you do, that marriage based on biblical precepts is frozen in stone and cannot develop or change is to ignore reality."
If passed, the bill would give gay couples officially recognised by marriage the legal right to adopt children. The Marriage Act 1955 restricts marriage to that between a man and a woman.
Anglican vicar the Rev Glynn Cardy, of Auckland, said the bishops' letter was an attack on gay, bisexual and transsexual people.
It contained misinformation and "questionable teaching" from scripture, including an interpretation of the Adam and Eve myth that implied marriage was between one man and one woman.
"The text was used by Jesus to prohibit divorce, a position most churches have repudiated, but was not to promote a nuclear family of dad, one mum and kids."
Presbyterian minister the Rev Margaret Mayman, of St Andrew's on The Terrace, said the bishops claimed homosexuality was unnatural. She was concerned their comments implied that children raised in non-heterosexual families were not in proper families.
"This is a civil and legislative issue and we do have our theological views, but we shouldn't be promoting social and legal discrimination."
The bishops are now preparing a submission on the bill.