Church leaders will use their Sunday sermons this month to implore their congregations to speak out against gay marriage.
With three weeks left for submissions on the bill to legalise gay marriage, the New Zealand Christian Network has asked members to write to the Government in opposition of the law change.
In an email to be "read out in churches" this month, the network encourages Christians to "take time to seek God's heart before writing their submission with grace and truth".
National director of the New Zealand Christian Network Glyn Carpenter said it was "highly probable that this bill will not be good for New Zealand".
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"This bill on its own will not bring about the destruction of society as we know it," he said.
"Marriage is already facing a number of challenges, and anyone with an ounce of common sense can see that families and society are weaker and poorer as a result.
"What politicians should be doing is looking at what needs to be done to strengthen marriage, not spending time debating bills whose main outcome would be to further undermine it."
Mr Carpenter urged anyone concerned by gay marriage to write a submission opposing it "and to do so with language and a tone of voice that is gracious and respectful".
"It is possible to talk so much or speak so loudly that people can't hear what we are saying," he said.
"It is also possible for language to reflect a tone of voice which does not communicate the love we are called to display."
The Marriage (Definition of Marriage) Amendment Bill to allow same-sex couples to wed has already passed its first reading in Parliament.