A Christian lobby group has caused offence by grouping same-sex marriage with incest in its submission against the Marriage Amendment Bill.
Family First presented its Protect Marriage petition with 72,000 signatures to a select committee hearing on the bill in Auckland on Tuesday.
In a heated discussion, committee member and Labour MP Moana Mackey questioned Family First on its submission and its comparison to incest.
Ms Mackey said she found it very offensive that the group compared same-sex relationshipsto something illegal.
Family First national director Bob McCoskrie replied that if marriage was made equal that would mean polygamy, and a father wanting to marry his daughter would eventually become legal also.
Mr McCoskrie said his group's opposition was not discrimination. He said he hopes the petition would let MPs know how people really feel, and that it is clear most don't want the concept of marriage to be redefined.
Mr McCoskrie says signatories support marriage remaining between one man and one woman and the incredible response shows the huge level of opposition to the bill.
"Marriage rightly discriminates. A 14-year-old cannot get married, three or four people cannot get married to each other, a person who is currently married cannot marry another person, a father cannot marry his adult daughter.
"Even those wanting equality believe there should be restrictions. This amendment bill has restrictions."
The petition had gained 48,000 signatures at the time of the bill's first reading.