Labour Party leader Andrew Little has given senior MP Phil Goff special dispensation to allow him to cross the floor over the Trans Pacific Partnership (TPP).
The Labour Party has made it clear it will not be supporting the trade deal in its current form.
Mr Little, who had previously refused to say whether or not the party would support it, said the deal went beyond trade and was an attack on democracy.
However Mr Goff has been at odds with that stance.
He said as former trade minister he started the negotiations for the TPP and he supported opening markets for exporters.
"I'm respectful of Labour's position on it (but) I have on record taken a somewhat different position."
Mr Little said he was happy for Mr Goff to publicly express that view, due to his historic involvement in negotiating its predecessor, the P4.
"Phil has had a long-standing involvement and public commitment to this agreement which differs with the Labour Caucus' decision that it cannot support the deal in its current form due to its compromise of New Zealand's sovereignty," he said.
"When the caucus met recently to finalise its position on the TPP I met with Phil and decided that his long-standing public position was such that he would be allowed to hold a differing view."
Mr Goff said he appreciated his leader's dispensation.
"I respect Andrew's and Labour's views on the issue and their agreement to acknowledge that I came from a different perspective.
"My position is well known and there is no need for me to elaborate further on it."
Mr Little said the TPP, set to be signed in Auckland next week, undermined the sovereignty of Parliament by preventing a future government from banning foreign buyers from the housing market.
He said Australia and other signatories of the deal were able to negotiate terms putting a limit on housing sales to overseas speculators.
"Labour supports free trade but this agreement goes beyond trade and is an attack on our democracy. That is why we cannot support it in its current form," Mr Little said.
Another MP, Damien O'Connor, said Labour MPs had a robust and healthy discussion on the deal.
"Labour as a party has always supported increasing trade opportunities but in this particular situation my personal view is that we can't trust [Trade Minister] Tim Groser and [Prime Minister] John Key to have done the best deal for New Zealand in the long term," Mr O'Connor said.
Fellow Labour MP David Shearer said he personally supported the TPP but said he would be voting with his Labour party colleagues along party lines.
Mr Key said it would be inconceivable for New Zealand not to be part of the TPP.