The body representing Scotland’s university principals has said students may have to pay towards the cost of their degrees after they graduate.
Universities Scotland said higher education should be “free at the point of entry and throughout their study”.
But graduates earning reasonable salaries should be asked to pay.
The principals are worried that Scottish universities are beginning to fall behind the standards of their counterparts in England.
A recent review of university funding in England, conducted by former BP boss Lord Browne, recommended that the cap on tuition fees, currently set at £3,290, could be removed altogether.
Graduates in England currently start paying their loans when they earn £15,000.
Scottish students studying in Scotland do not have to pay tuition fees.
Alastair Sim, director of Universities Scotland, will tell an education conference in Edinburgh that they should not pay until they have graduated.
He will say: “A contribution sought from graduates must be set at a level that does not discourage participation and students from all backgrounds must be able to study any course at any institution.
“Academic potential, and not the ability to pay, must be the determining factor.”
Universities Scotland is also calling for the establishment of an expert group to model and cost a “workable” graduate contribution immediately after the publication of the Green Paper on university funding later this year.
Earlier this month, Sir Andrew Cubie – who chaired a landmark inquiry into student funding a decade ago – said Scotland’s system of university funding was unsustainable without some contribution from graduates.
In Scotland, tuition fees were abolished in 2000, two years after their introduction by the Blair government.
A one-off graduate endowment fee of just over £2,000 was scrapped by Scottish ministers in 2008.
In his speech in Edinburgh, Mr Sim will also warn against short-term budget cuts.
He will argue: “If we see major cuts in university funding in this year’s budget bill, there will be effects which damage Scotland economically and socially.
“Many of these cuts are not quickly reversible and there is no credible way in which income from other sources can fill the gap next year.”
He will also say that cuts in line with the government’s independent budget review would mean fewer Scots being able to access university education, a reduced choice of courses and “substantial” job losses.
Scotland would also lose leading researchers to competitors and lose its reputation as a popular destination for international students.
Education Secretary Michael Russell, another speaker at the conference, said earlier this month that “there will have to be major changes” but has ruled out upfront tuition fees.
The Scottish government said it was “committed to protecting the reputation and quality of our universities”.
A spokeswoman said: “However we now know that as a result of the UK Government’s decisions, Scotland’s resources will be cut by £1.3bn next year.
“We will work to build consensus for a budget bill that protects frontline services, sustains economic recovery and builds a low carbon economy.”
The Scottish Labour Party said Universities Scotland’s position was “a further hammer blow to the SNP’s unsustainable approach”.
Labour’s further and higher education spokeswoman, Claire Baker, said: “Students and principals realise that we can’t go on as we are and something needs to be done sooner rather than later.
“People want urgent action from this government on this issue and it has been severely lacking.”
Her party has called for an independent review to resolve the “crisis”.
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