Doctors are concerned Medicare rebate changes for some private surgery procedures will create "chaos" for patients.
The changes under the Medicare Benefits Schedule will affect orthopaedic, general and heart surgery and come into effect on July 1.
More than 900 MBS items will be affected but the Australian Medical Association says a lack of detail has been provided to doctors and health funds.
"The AMA is concerned that the private healthcare sector - including health funds, hospitals, doctors and patients - will not be ready for the July 1 changes due to poor implementation by the government," AMA president Omar Khorshid said on Sunday.
The federal government established a taskforce to assess the rebates as part of the most thorough review of Medicare in 30 years.
It said the taskforce had consulted widely and received feedback from thousands of stakeholders.
Dr Khorsid said the first tranche of MBS changes in 2018 had created uncertainty for doctors and patients because private health insurers didn't have their schedules updated in time.
"Patients were left out of pocket, spinal surgeries were delayed, and doctors couldn't provide patients with informed financial consent about potential gap fees," he said.
"More than two years later, we are facing the same problems but with more than ten-fold the volume and complexity.
"We simply don't know what the rebates from funds will be, as they haven't had the time to prepare and release them in advance - including for surgeries already booked for next month."
The AMA wants a six-month lead time to prepare for the implementation of such changes.
Dr Khorsid also called on the government and private health insurers to ensure patients were not worse off financially for undergoing surgery after July 1.
Health Minister Greg Hunt said there had been a "long lead time" for the changes, many of which dated back to last year's budget.
He said the federal government was investing a further $6 billion in Medicare services over the next four years.
"We work very constructively with the medical groups and follow medical advice of the taskforce and the medical services advisory committee," he told reporters.
"It is focused on patient safety, patient services, and patient outcomes."