The Greens say the Morrison government must abandon plans to shake up university fees in order to drive enrollments in priority areas, after Education Minister Dan Tehan's own department admitted there was limited evidence the proposal would work.
However Mr Tehan says past fee changes for maths and science courses resulted in a boost of 12,000 extra students over three years.
Department of Education deputy secretary of higher education, research and international, Rob Heferen told a Senate inquiry on Tuesday the department had not performed any modelling about how slashing fees for courses such as English, maths and science would impact on student numbers.
The changes are intended to drive enrollments in areas of skills shortages.
However Mr Heferen said past fee changes had drawn a "pretty muted" response from students.
"Will it be significant? Think so. When will we know? When we actually see what the enrollments will be," Mr Heferen said .
Greens' education spokeswoman Mehreen Faruqi said the proposal should be dumped.
"Not only are these fee hikes grossly unfair for students, there's actually no evidence that they will do what the government intends them to: encourage more students to take up STEM and other 'priority' courses," Senator Faruqi said.
"The government's package simply doesn't stack up.
"We've heard from key stakeholders across the sector that all it will do is put students further into debt and cut more funding for essential teaching and learning on campuses.
"As our universities continue to suffer huge job losses, now is the time to invest heavily in higher education, not take the easy way out and transfer costs from the government onto students. No one wins from the Liberals' cruel austerity package."
However Mr Tehan said there was strong evidence underpinning the proposed changes.
"The evidence was clear when we looked at it: when the student contribution for maths and sciences was reduced in 2009 the number of students applying to study science grew from 13,795 to 26,272 in 2012," Mr Tehan said.
"During COVID-19, universities rolled out microcredential courses to study in areas of national priority and the demand from Australians clearly exceeded our expectations.
"As well as changing the costs for courses, we are also changing behaviour by promoting careers in science, technology, engineering and maths and reforming senior secondary pathways to encourage students to pursue careers in areas of expected future job demand."
The government will need crossbench support in the Senate to get the changes over the line. Independent senator Jacqui Lambie has declined to say how she'll vote, while Centre Alliance's Rex Patrick said the party had made no decisions yet on the legislation.