A leaked paper indicates New Zealand negotiators are resisting a tough stance by the United States on copyright infringement and other intellectual property demands.
Some 400 from the nine countries involved in talks on the TransPacific Partnership (TPP) are in Auckland for meetings this week.
In previous trade deals, the United States has pushed for stronger enforcement of copyright for its film studios and longer patents for US pharmaceutical companies.
A paper leaked to a non-governmental organisation suggests New Zealand is unhappy with that approach in the TPP.
Former New Zealand trade negotiator Charles Finny says the US cannot be too demanding without making concessions of its own on agriculture.
Protesters greet delegations
About 40 protesters gathered outside the start of the trade negotiations at Auckland's Sky City, led by anti-globalisation group Global Peace & Justice.
One protester, Auckland University law professor Jane Kelsey, says American companies are pressuring negotiators to advance their own agenda.
She says the pharmaceutical company lobby wants to get rid of New Zealand's government drug funding agency Pharmac so they get higher royalties, which would mean this country's health dollar goes much less far.
Professor Kelsey says New Zealand is likely to get little better access to US markets from the deal, and, because negotiations are in secret, it is impossible to know what concessions negotiators have made until the agreement is signed.