Council of Trade Unions president Helen Kelly is to boycott next week's meeting of the United States-New Zealand Council.
The two-day meeting in Christchurch will be attended by senior US Government officials.
Helen Kelly, a member of the US-NZ Council, says the meeting will be a big lobby-fest for the proposed Trans-Pacific Partnership trade deal.
It will uncritically push for a deal regardless of the content, she says, but unions in all the countries involved have concerns about labour rights.
Ms Kelly says she would be a lone voice expressing disquiet, so has decided not to attend.
Foreign Affairs Minister Murray McCully says US Secretary of Homeland Security Janet Napolitano, who was to have attended the meeting, has cancelled because of the fatal shooting of an immigration and customs agent in Mexico.
Mr McCully says he has conveyed his sympathies to Ms Napolitano and extended an open invitation for her to visit in the future.