TRADE Minister Andrew Robb has made market access for Australian farmers, including into the United States, Canada, Japan and Mexico, a key bargaining point in the Trans-Pacific Partnership (TPP).
But politically-connected US sugar growers are lobbying furiously against facing more competition from foreign growers.
The TPP is a proposed major trade and investment accord covering more than 40 per cent of the world's economy. It aims to set sweeping new rules for trade and investment in relations to tariffs, quotas, intellectual property, labour, the environment and state-owned enterprises.
US President Barack Obama overcame raucous opposition from unions and his own leftist Democratic party in June to secure authority from the US Congress to conclude the TPP details with the 11 other Pacific Rim countries.
US Trade Representative Michael Froman said the US and Japan - the pact's two major participants - still had differences to overcome on market access for farmers and car makers.
"Canada market access in the agriculture area remains a very important outstanding issue," he said.
Trade sources close to the talks say Canada has been holding out on opening up its agricultural market to foreign competition, especially the highly protected dairy sector that Australia, New Zealand and the US want to sell more produce into.
Australian cane growers can sell a relatively paltry 87,000 tonnes of sugar in the US. American producers are guaranteed of supplying at least 85 per cent of domestic sugar demand under the government's sugar program.
Politically influential growers, including in the key swing state of Florida, hold enormous lobbying sway over American politicians, who are preparing for elections in November 2016.
Mr Robb said negotiations on sugar have been "tough and are still on the table for resolution".
"I'll continue to push hard in the coming weeks for new levels of meaningful access for the Australian sugar industry, not only with the United States but with other partners as well," Mr Robb said.
The US had a domestic sugar production shortfall of about 400,000 tonnes last year, allowing for existing imports from other countries.
Last month, Australian trade negotiators were pushing to be permitted to fill around half, or 200,000 tonnes, of the sugar deficit. But the US has been resisting that moderate demand.
Seeking sugar inclusion: Canegrowers
The Australian Canegrowers group said Mexican growers could not meet the projected increase in US sugar import demand, so sugar should be fully included in the TPP.
"There is no reason why unsubsidised Australian sugar should have lesser access to the US than Mexican sugar, which has been found to be subsidised and dumped into the US," Canegrowers economics head Warren Males said.
The US recently slapped an anti-dumping import ban on Mexican sugar.
Meanwhile, leaked draft chapters of the TPP text imply the US will win extra international IP rights for their drug producers.
Responding to criticisms that the US was lobbying on behalf of "big pharma" to push up the price of medicine and block affordable access to the poor, Mr Froman said "we want to incentivise the development of life-saving treatments" but "ensure there is access to affordable medicines in developing countries".
Trade ministers are hoping to finalise the TPP in the second half of this year but must still overcome differences on the most politically sensitive areas, such as agriculture and intellectual property.
"We're in the final stages of negotiating the Trans-Pacific Partnership," Mr Froman said.
"We're down to a reasonable number of outstanding issues, but by definition those issues tend to be the most difficult, whether it's about market access or rules about intellectual property."