Patients who are "frequent flyers" might bypass their local doctors and land in hospital emergency departments instead if GP co-payments are introduced, South Coast GP Brett Thomson has warned.
Co-payments of up to $6 to visit the doctor have been flagged by the federal government as one way to tackle rising health spending.
While Prime Minister Tony Abbott has downplayed concerns his government might introduce GP fees, Health Minister Peter Dutton has said Medicare is unsustainable and the better-off might need to pay more.
"A lot of doctors in this region do charge some people a payment on top of what they get rebated from Medicare," Dr Thomson said.
"But we still bulk-bill a significant proportion of our patients - the bulk-billing rates around the country are over 90 per cent - and some of these people will think twice about going to the doctor's if they have to pay.
"It will particularly affect those who need services the most, the 'frequent flyers' - people who have chronic conditions and need to be seen regularly and who quite often are struggling financially."
Dr Thomson was concerned that people would put off going to the doctor and get sicker, or head straight to emergency departments.
"We've got a busy emergency department at Milton and I know the other EDs in the Illawarra do see lots of category four and five patients, which are akin to GP presentations," he said.
"If there are disincentives to visit GPs, it could well be seen as putting pressure on EDs."
Dr Thomson was also concerned that co-payments could put pressure on medical practices, which might feel forced to absorb the cost.
"So patients won't be making a co-payment; those practices will be accepting a lower fee to do the same amount of work," he said.
"We mustn't further erode the viability of [general practice] as a career choice for doctors."
NSW Nurses and Midwives Association regional organiser Mark Murphy said the union opposed any attacks on Medicare.
"We've got a system in Australia where everyone has access to free health and, in the association's view, that is a right, not a privilege," he said.
"Some might say that $6 is not much, but that's just the beginning."