Trade Minister Tim Groser says a future Labour Government could withdraw from the Trans-Pacific Partnership Agreement (TPPA) if it wanted to, but it would be at a high price.
Labour recently announced it won't support any deal that would prevent a ban on foreign property buyers or threatens drug purchasing agency Pharmac's ability to drive down the cost of medicine.
If he gets into power, leader Andrew Little says he will try to fix it or pull New Zealand out altogether.
Mr Groser is currently in Hawaii for the negotiations, which are entering their final stages.
"There is no trade agreement that a future New Zealand government can't decide, 'Sorry, I don't like this – I'm withdrawing,'" he told the Paul Henry programme this morning.
"The problem with that is that when you withdraw, you also lose all the benefits of this agreement."
Mr Groser says the 11 other Trade Ministers in Hawaii are optimistic an agreement can be reached in the next week.
The 12-nation agreement has been touted as bringing New Zealand a potential $4 billion trade payoff, but opponents have criticised the secrecy in which it's being done.
It will only be presented to Parliament for a vote once it has been signed, and Mr Groser says the talks can't take place in public.
"This is a moving game, and we need adults to do this – not breathless children to run off at the mouth when the deal is not actually finished."
Prime Minister John Key admitted yesterday the Government may have to spend more on medicines under the TPPA, but the costs will be covered by increased economic activity.