Trade Ministers may be flying into the country next week to sign the Trans-Pacific Partnership agreement - but opponents are assuring the public this is far from a done deal.

Four opposition parties have slammed the agreement at a public meeting in Auckland.

Metiria Turei spoke on behalf of the Green Party, Grant Robertson for Labour, Marama Fox for the Maori Party and Fletcher Tabuteau for New Zealand First. 

The general consensus was that the deal undermines New Zealand's sovereignty.

Green Party co-leader Metiria Turei told those gathered that the whole point of the deal is to take power away from democratically elected governments, and give it to multi-national corporations.

She says where their interests clash with what's best for New Zealand, it's clear the investors will come out on top.

Ms Turei says it's not about trade - it's about power.

US global trade activist Lori Wallach told the crowds the deal offers very little upside for our country, and enormous downsides - including increasing prices for PHARMAC, yet New Zealand's been one of the most enthusiastic.

Ms Wallach said the agreement is far from a done deal - currently lacking majority support in the US Congress.

She spoke at the Auckland Town Hall tonight - the first of a series of nationwide public meetings - and says Tim Groser's not telling everyone back home there's no majority support in the US Congress in favour of the TPPA.

Ms Wallach said the US President could sign a trade agreement in blood, gold or ink - but if Congress does not approve it, it's nothing more than a five thousand page doorstop.