Psychologists are urging the federal government to reverse a decision to slash subsidised mental health sessions in half.

The changes are due to come into place on January 1 and would reduce the number of Medicare subsidised psychology sessions from 20 to 10.

During the COVID-19 pandemic, the former coalition government allocated funding for the additional appointments to help address the mental health effects of lockdowns.

The Labor government has decided not to renew the funding because Health Minister Mark Butler said the scheme had extended waitlists and become a barrier to more people being able to access mental health treatment.

But two leading psychologist groups said positive findings from the government's review of the scheme had been ignored.

The Institute of Clinical Psychologists (ICP) and Australian Clinical Psychology Association (ACPA) called on Mr Butler to reconsider his decision.

ACPA professor Caroline Hunt said the government's review had found most mental health conditions needed more than 10 psychological sessions to be treated.

Prof Hunt warned psychologists would have to turn away people with moderate and severe conditions.

"Delivering only half a treatment would be unethical, likely resulting in relapse or a worsening of the condition," she said.

"We believe halving access to quality psychological interventions when we do not have alternative options in place is a mistake."

Labor backbencher Josh Burns spoke out against the decision when it was announced earlier in December.

Mr Burns said the answer to managing access to mental health services was not to reduce support for people who need it.

ICP president Dr Marjorie Collins agreed and said evidence showed reducing rebated sessions would lead to poorer community health outcomes

The government plans to overhaul mental health care in Australia but the two groups said continuity of patient care was essential while that was under way.