Leaked documents show New Zealand has agreed to let foreign investors sue the Government in overseas courts.
The draft text of the TransPacific Partnership shows Australia has refused to sign up to that part of the deal.
TPP critic Jane Kelsey says the partnership is the only opportunity for the country to have a free trade agreement with the US.
"Therefore there is a real risk that the Government will agree to almost anything that is put on the table by the US unless it is a price that considered politically too high to pay, which appears to be the case with Pharmac."
Ms Kelsey says New Zealand is at risk of being sued by companies such as Philip Morris, Pfizer, Warners or Microsoft.
The Greens want the Government to get itself out of the deal.
Co-leader Russel Norman says it's much better for New Zealand to be able to regulate without being sued by foreign corporations.
"At this stage nothing's been signed off by the New Zealand Government and so it's entirely possible for us not to sign up to these investor state disputes clauses."
The Greens say for example, it'd give tobacco companies more power to pressure our government over planned anti-smoking initiatives.
Co-leader Russel Norman asked Trade Minister Tim Groser if the government will release the text of the agreement so the public can see what's in it and the position taken by New Zealand in negotiations.
"And no, and certainly not without the consent of our negotiating partners."