A trade academic says Japan's entry to the TransPacific Partnership talks will delay any deal by several years.
University of Auckland law professor Jane Kelsey says New Zealand agricultural industry groups celebrating Japan's entry should think again.
Professor Kelsey says some of those in the Canadian and US agriculture sectors believe Japan's presence at the negotiations may may help them resist demands for agricultural trade concessions.
Others, she says, believe the prospect of more export opportunities to Japan will reduce US anxiety over the threat from Australia and New Zealand.
"There's a sort of chess game going on," she says. "There's a whole lot of hypotheticals flying round there and anyone who thinks that any of those would play out easily ... needs to have a hard rethink."
Professor Kelsey says the Japanese public and politicians are very concerned about issues such as intellectual property, food safety and agriculture.