Federal Health Minister Peter Dutton says figures about the number of people who will attend hospital emergency departments if a GP copayment is introduced have been "cooked up".

The New South Wales Health department found there would be an increase of 500,000 people visiting the state's emergency departments if a $6 GP copayment was enforced.

A spokeswoman for New South Wales Health Minister Jillian Skinner said the modelling was conducted before the Federal Government put forward its proposal for a $7 copayment.

Mr Dutton said the report was not credible.

"Not even Labor premiers have suggested anything like the numbers that have been cooked up by obvious union sympathisers within the New South Wales Health Department," he said.

The Federal Opposition has seized on the report, with Labor's assistant health spokeswoman Jan McLucas saying it has wider implications.

"What New South Wales has revealed will occur in every other state or territory-run hospital system," Senator McLucas said.

"It stands to reason, if you put a price on going to the doctor, and a person is poor, on a very low income, and sick, they will find a way to go to the doctor that avoids that tax."

Senator McLucas said there would also be an impact on people who lived outside metropolitan areas.

"It's not only in the capital cities - it's particularly the case in regional centres, where we have low income levels," she said.

"Those public hospitals in those cities and regional centres, we know, will also be affected by this dreadful tax."

Ms Skinner said the Opposition was running a scare campaign on the issue.

"The NSW Ministry of Health has undertaken no detailed modelling on potential impacts since the Federal Budget, handed down in May," she said.

"I have not commissioned any modelling."

Mr Dutton said the Government was determined to make Medicare sustainable.

"I notice Minister Skinner has put out a statement to dismiss the report," Mr Dutton said.

"I don't think it needs to be given much credibility. The Government's obviously determined to make Medicare sustainable."

He said Australia had an ageing population and needed to tackle rising costs.

"At the moment four out of five presentations at doctors surgeries are free," he said.

"That is just not sustainable."

The Federal Parliament is yet to pass legislation enacting the $7 co-payment for GP visits.