A national march, spanning at least 15 New Zealand towns and cities, will take place today in opposition to the Trans-Pacific Partnership Agreement (TPP).
The TPP is a free trade agreement proposed between 12 Asian and Pacific countries, including New Zealand and the United States.
Protests will take place in 15 cities including Auckland, Wellington, Christchurch, Hokianga, Whangarei, Hamilton, Taranaki, Tauranga, Whanganui, Palmerston North, Nelson, Geraldine and Invercargill.
Politicians, activists, academics, union staff and business people will be among the speakers at today's protest.
Activist network behind today's protest, It's Our Future, said communities would march to express opposition to the secrecy of the TPP negotiations and the potential threat it posed to New Zealand's national sovereignty.
It's Our Future spokesperson Edward Miller said there was an ''unprecedented groundswell'' of public concern over the agreement.
Miller said he expected at least 1000 people to join the march in each of the country's main centres.
There was always a concern people might become hostile during a big march but he hoped New Zealanders would express their views ''democratically and peacefully''.
It's Our Future said documents relating to the agreement were secret.
However, enough was known to show the TPP could impact on a ''broad range of life'', including giving foreign investors the rights to sue the Government over tighter mining laws or tobacco control and stop the establishment of new state-owned enterprises.
University of Auckland professor Jane Kelsey said the TPP negotiations had already taken four years without any resolution.
The film and television industry would also voice its opposition to the TPP today.
Actors' Equity vice president Jeff Szusterman said the Government should reject the TPP because it would allow the US to get total market access for their film and television output while New Zealand performers were pushed off the screen.
However, Government ministers have repeatedly said the deal will be beneficial to the New Zealand economy by opening up trade opportunities.
Today's march follows a campaign last year to oppose the secrecy of the TPP.