Labour's Janet Mackey has accused gay MPs of hijacking the Civil Union Bill and making it into their own issue.
Ms Mackey, the MP for East Coast, was in Australia when the bill passed its first reading on Thursday and did not vote.
She said yesterday she intended taking part in futuredebates on the bill but she was unhappy about the way it was being presented.
"I think it's unfortunate that a couple of gay members of our caucus have chosen to hijack the bill and make it an issue for and about gay people," she said.
"It is not, but this has made it difficult for me to take it back to my electorate."
Parliament's two openly gay MPs, Chris Carter and Tim Barnett, are strong supporters of the bill and both made emotional speeches in Parliament this week.
Ms Mackey said the bill was about people generally "who simply want a civil rather than a religious marriage".
She said she did not have a problem with that, nor did she have a problem with a civil union being open to same-sex couples.
She echoed National Party complaints when she said she believed the Government was "spending more time engaged in social engineering than on good legislation and I think that is reflected with this bill".
Several National MPs said the same thing during Thursday's debate.
"I don't believe it is the role of any government to legislate values," she said.
"Communities themselves should determine the values that are appropriate to them, then go to government with what they have decided."
Mr Barnett would not comment on Ms Mackey's "hijack" remark.
"I wouldn't ever respond to colleagues who criticise me in public."
He said the bill was a conscience issue for his party.
