Leading U.S. lawmakers are urging the Obama administration to exercise caution before admitting Japan into talks for a major free trade partnership.

Japanese Prime Minister Yoshihiko Noda is expected to announce whether his country will apply to join the Trans-Pacific Partnership talks before he leaves this week to attend a regional economic summit in Hawaii.

The talks are aimed at eliminating all tariffs on trade between the United States and eight other Pacific Rim countries. But in a formal letter Tuesday, the lawmakers argue that Japan has numerous non-tariff trade barriers embedded in its economy.

The legislators say any trade deal involving Japan will require robust rules to address those barriers. They say Tokyo’s participation in the talks would add “dramatically new dimensions and complexities.”

The letter is signed by the top-ranking member of each political party on the House and Senate committees that deal with trade issues. They urge U.S. Trade Representative Ron Kirk to consult with the U.S. Congress and other interested parties well in advance of making any decisions.

The TPP is also controversial in Japan, where farmers and other groups have long enjoyed protections against foreign competition. Thousands of farmers and fishermen rallied in Tokyo Monday to voice opposition to Japan’s participation in the pact.