More than 1 million Australians owe the federal government A$8 billion (£2.8 billion) in deferred university tuition payments under the Higher Education Contribution Scheme.
The debt for individual students seems set to increase sharply as a result of the government's reform plans. Australian vice-chancellors last week proposed that universities have the option of increasing fees and that these be covered by interest-free loans as with the Hecs system.
The government claims the amount owed by a student graduating with a three-year bachelors degree this year will be about A$15,000, which is then repaid via a tax surcharge when the graduate is earning at least A$23,000 a year.
Education department secretary Peter Shergold has said that higher Hecs charges are being considered. He told a convention in Melbourne that taking account of forgone earnings and the direct costs of a university education, the net monetary gain to graduates over a working lifetime was more than A$145,000.
The National Tertiary Education Union and the National Union of Students said they would fight any increase in Hecs.
The unions said the government should be providing more funds for higher education, not forcing students to pay even higher charges.
Dr Shergold said: "Many low-income taxpayers who will never have the chance to go to university will pay for the private financial benefits that accrue to those who, as a result of higher education, will be high-income earners in the future."