The Castlemaine Medical Group represents the town's 21 general practitioners and has drafted a letter to Prime Minister Tony Abbott, expressing concern about the proposed budget implementation.

Group spokeswoman Dr Louisa Hope said a co-payment would put additional strain on public hospitals and emergency departments.

"A co-payment would end universal access to healthcare regardless of ability to pay," she said.

"It will push a lot of vulnerable people who can't afford the co-payment onto the public hospitals and the emergency departments of the public hospitals and some people will miss out on the treatment they need.

"That's particularly relevant for us because in Castlemaine the GPs provide the after hours service so we'd anticipate actually seeing fewer patients during the day and then having to treat them after hours.

"it's already onerous to provide the after hours service and to have that load increase ..."

The letter has been signed by the 21 GPs and will be sent to Prime Minister Tony Abbott, Treasurer Joe Hockey, Health Minister Peter Dutton and 76 senators.

"We just want to be heard," Dr Hope said.

The letter expresses the group's "dismay and deep disappointment" about the proposal.

"It will have a profound impact on the health of many Australians, particularly those with the least capacity to pay, who often have the greatest healthcare needs," it reads.

"A co-payment will undermine the important general practice principle of disease prevention which keeps people out of the costlier hospital system.

"The Australian Government has failed to keep its pre-election promise of no funding cuts to health and has ignored the expert advice of major Australian health bodies, including the RACGP, who joined forces to reiterate that this model will not result in government savings.

"In fact, it will achieve the opposite."

Castlemaine GP Sheriden Emonson said for many patients a bulk-billed appointment with a GP was their only connection to emotional, psychological and physical support. 

"My personal opinion is that  I do not support the $7 co-payment," she said.

"Much of general practice work involves meeting complex care needs of our community.  

"I believe that by introducing a $7 co-payment, many of our patients will be less likely to attend regularly to their GP for preventative health needs, chronic disease management and ongoing mental health care."