Medical fund will reduce debt: Govt

The government is again defending its proposed GP co-payment, saying the policy is an "essential structural reform" that will reduce net debt.

Finance Minister Mathias Cormann says the fund will stay as an asset on the government's balance sheet in perpetuity, reducing debt by $20 billion once it has accumulated.

Only the investment returns are spent on medical research, he says.

The government is facing backlash over the policy, with Labor, the Greens and key crossbenchers opposed to the amount and the scope of the charge.

The Australian Medical Association has proposed a Medicare co-payment of $6.15, and says concession card holders and those under the age of 16 should be excluded.

But Senator Cormann says a price signal is necessary for the healthcare system to support an ageing population, and excluding pensioners would defeat the purpose.

"The truth is that those most likely to need access to high-quality healthcare services in the future are also those who most need this reform package to successfully pass the Senate," he wrote in an opinion piece in The Australian.