Doctors' groups want to make the freeze an election issue and are encouraging their patients to complain to local MPs.
Mr Shorten stepped up his attack on the government decision while campaigning in northern NSW on Sunday. He said eroding subsidies for GP visits was a "disaster" for patient care because doctors would pass the extra costs on to patients.
"You cannot trust the Turnbull coalition with Medicare," Mr Shorten said. "They want to freeze the rebate, which compensates for rising health-care costs, well into the future. Doctors are saying that will force them to introduce a backdoor tax."
Mr Shorten has taken such a strong stance on the issue it is difficult to see how he could not announce removal of the freeze. But he said he would not reveal details of Labor's health policy until later in the campaign. It was Labor that introduced the rebate freeze in 2013 and the Coalition left it unchanged."