That would challenge Pharmac's decision-making process, he said.
"The way Pharmac operates with its buying power assists New Zealanders get affordable access to medicines.
"The Government should not sign a trade deal that pushes up the price of medicine for New Zealanders in order to give new rights to US pharmaceutical companies."
Labour's Acting Health spokesman David Clark said Pharmac was a "bright light" in the health sector, that saved Kiwis millions of dollars by negotiating cheaper medicines.
"Now John Key is looking to take more money out of the health budget to pay for multi-national corporate welfare."
NZ First trade spokesman Fletcher Tabuteau said the Government needed to provide reassurance that New Zealanders would not be "clobbered" by big drug manufacturers.
Pharmac is a Crown agency that works with District Health Boards to decide which medicines and related products are subsidised for the public.
A spokesman for Trade Minister Tim Groser said the Government does not comment on rumours of purported leaked texts in TPP.
However, Mr Groser has in the past said that negotiators were working to get the best deal for Kiwis, and that it would not negotiate on the fundamentals of the public health system.
Dr Graeme Jarvis, general manager of Medicines New Zealand, which represents companies involved with the development, production and prescription of medicines and vaccines, said changes suggested by the Wikileak would be positive.
"We are not seeking an end to Pharmac, but what we have said is there is significant room for improvement, in the transparency of Pharmac's decision-making process and the timeliness of the funding decisions.
"And it seems to me that what has been proposed in this Wikileak is along that similar line."
Dr Jarvis said proposed changes to Pharmac would probably not undermine the agency's effectiveness. Irrespective of the TPP outcomes, he said currently New Zealanders were having to wait for up to eight years to get some cost-effective medicines from Pharmac.
However, Professor Jane Kelsey of the University of Auckland said the documents showed that Pharmac was the "most exposed" of any programme in a TPP country.
Ms Kelsey said there were numerous ways the US and overseas pharmaceutical companies could undermine Pharmac's effectiveness as a result, including restricting cheaper generic medicines.
The US could potentially refuse to bring the TPP into force in New Zealand until Pharmac's regulations were changed to match the Annex, she said.
