Prime Minister John Key says New Zealand will not sign up to the Trans Pacific Partnership unless dairy products are included in the trade agreement.
Negotiations on the TPP will continue in Auckland next month, after leaders including President Barack Obama signalled their commitment to concluding a deal in Cambodia last week.
Mr Key says one point of negotiation is the abolition of US tariffs on dairy products.
"We're not prepared to see dairy excluded. And in terms of abolition, yeah, I mean that's the aim. There might be a time frame under which clearly there'll be a phase out. But in the end New Zealand can't sign up to the TPP if it excludes our biggest export."
Mr Key says the retention of the drug-buying agency Pharmac is also important for New Zealand in the talks.