Conservative Party leader Colin Craig has sparked outrage by saying homosexuality is a choice and gay people are more likely to have been abused as children.
The comments on TV3's The Nation this morning came in a discussion with Labour MP Louisa Wall over her bill to legalise same-sex marriage.
Asked if he thought the bill might encourage homosexuality, Mr Craig replied people chose to be homosexual and factors other than genetics could determine whether someone was gay.
"I think most people recognise that there are other influences such as upbringing, such as events in life," he said.
"For homosexuals, they are statistically far more likely to have suffered child abuses as a child... It certainly can make a difference in someone's choices in life, there's no question about that in my mind."
Mr Craig said he was not worried the bill would fuel homosexuality, because it was a personal choice.
Ms Wall responded: "Homosexuality isn't a choice Colin, people are born the way they are born."
Mr Craig's comments sparked an immediate backlash on Twitter.
Claudette Hauiti described the comments as dangerous, homophobic and ignorant.
Kaine Thompson tweeted: "How can Colin Craig get away with saying homosexuality comes about because of child abuse?"
Bruce Buckman tweeted that Colin Craig would have campaigned against women's suffrage in the 1890s on the grounds that it "undermined institution of democracy".
Ms Wall told The Nation her bill would recognise the equality of people's citizenship in a modern democracy.
"What my bill seeks to do is to allow two people - regardless of their sex, sexual orientation or gender identity - to marry within the institution of love that I think marriage is."
Ms Wall said marriage was the primary focus of the bill, but by virtue of the definition, married same-sex couples would be able to adopt.