The federal government has hit back as a key US senator accusing Australia of being "greedy" threatens to reject the Trans-Pacific Partnership deal.

US Senate Finance Committee chairman Orrin Hatch, a Republican whose support will be crucial to passing the deal, is unhappy that intellectual property protections for biologic medicines have not been extended to 12 years.

The proposal would have made life-saving medicines more expensive for Australians and Trade Minister Andrew Robb says he was never going to accept it.

"We have absolutely no intention of increasing the cost of medicines to the Australian public by seeing any increase in the period of data protection," Mr Robb told AAP on Saturday.

Australia now has a five-year data protection period rule, which protects the makers of biological drugs by blocking other manufacturers from relying on their research to produce a copy of the product, known as a biosimilar.

Hatch says Australia has been "greedy" in resisting the longer monopoly period and that the US should never have agreed to it.

He says he will carefully study the text of the deal, released on Thursday night, but suggested negotiators might have to go back to the table.

"I understand that renegotiation may be difficult, particularly with so many parties involved," he said in a speech at the US Chamber of Commerce, which has yet to give a verdict on the pact.

"But at the end of the day, the alternative to renegotiation may very well be no TPP at all."

Some of President Barack Obama's Democrats have also suggested renegotiating the deal.

Mr Robb says Australia's resistance was "strongly supported" by the majority of the 12 nations involved in the negotiations and was ultimately accepted by all parties.

But health experts have argued the wording of the deal is "worryingly ambiguous and unclear" and appears to give the US scope to pressure Australia into keeping cheaper biosimilar medicines off the market for eight years.

Dr Deborah Gleeson, public health lecturer at La Trobe University, says that would drive up the price of medicines, which can already cost up to $150,000 per year for both patients and the federal government.

Mr Robb has insisted Australia did not move "one iota" on the issue and has protected the five-year rule.