Negotiations for a regional free trade deal, which would include the United States, have hit a snag which could cost New Zealand dairy farmers free access to the world's biggest market.
The US wants existing trade agreements between the eight countries negotiating the TransPacific Partnership left in place.
Trade Minister Tim Groser says that could make it harder for New Zealand to better a deal Australia signed with the United States seven years ago.
The Dairy Companies Association says New Zealand farmers want better access to US markets than Australians got in their deal in 2003.
The US had signalled that it would negotiate a single agreement with the eight countries in the TPP.
Now it wants to negotiate separate deals within the TPP with New Zealand, Vietnam and Brunei, and leave existing agreements with others like Australia untouched.
Radio New Zealand's economics correspondent says a lot is riding on the talks after G8 countries left the Doha round of world trade talks in tatters at the weekend.