Key members of the United States food industry have come out in support of comprehensive free trade deal including New Zealand.
The eight countries in the TransPacific Partnership, or TPP, began the second round of negotiations in San Francisco on Monday.
Food giants Nestle and Walmart are among 26 signatories to a letter to the US Trade Representative and Department of Agriculture.
In it, they warn protecting US special interests in negotiations could cost its exporters free access to other TPP countries' markets.
US lawmakers received a letter earlier this year warning of the potential cost to American farmers of opening markets to food imports from New Zealand.
The US-New Zealand Business Council's Stephen Jacobi says this most recent letter comes from a powerful group.
But he doesn't expect it to quell opposition to a comprehensive deal from US farming lobbies.