A law professor observing the Trans-Pacific Partnership negotiations in Salt Lake City says American negotiators are intent on curbing Pharmac's negotiating power to stop other countries adopting its innovative approach.
Professor Jane Kelsey of the University of Auckland says the United States has adopted a strategy of exhaustion to force the other 11 countries taking part to acquiesce to their demands.
She says the US is bullying negotiators, as it moves towards the end point of TPP talks in December.
Professor Kelsey says the US wants tougher copyright and patent rules on medicines and to stop access to cheaper generic ones.
She says it is targeting Pharmac, which buys generic drugs, as it is seen as undermining the profits of large US pharmaceutical companies.
Professor Kelsey says Australia and other countries are keen to adopt New Zealand's approach and the United States wants to prevent that.
She says the negotiators are working from morning until late at night. While the US has about 20 people who can rotate, some countries have only one delegate.
Professor Kelsey says if the US pushes through the measures it wants, the pharmaceutical industry will have more influence over the internal decision making processes and criteria of Pharmac and other medical buying agencies.
A spokesperson for the Ministry of Foreign Affairs and Trade says the Government has been very clear on its position that New Zealand is not prepared to negotiate on the fundamentals of the Pharmac model.
The spokesperson says negotiators are working hard to meet the objectives set by TPP leaders and ministers in Bali in October 2013.