Labour Party MP Louisa Wall is close to securing the support to legalise same-sex marriage, a Herald poll of MPs shows.
However, many MPs were refusing to commit to a decision on the marriage equality bill, and the final vote could come down to the wire.
A straw poll ofall 121 MPs found that fifty-four MPs have indicated they would support it at least in its early stages, or were considering supporting it.
New Zealand First this afternoon indicated that it might abstain from the vote, because it preferred to put the issue to a public referendum.
This would mean the bill would need 57 votes to pass.
New Zealand First leader Winston Peters said: "Serious issues like this should be decided by the public of this country and not a few temporary empowered politicians."