Fears grew this week that a Scottish degree will cost some students more than studying in England, after Aberdeen became the first university to announce it will levy maximum tuition fees.
From 2012 "rest of UK" (RUK) students attending Aberdeen University will have to pay the full pound;9,000 per year.
In a concession, the university will not charge for the final year of a standard Scottish four-year degree, capping the total cost at pound;27,000 - the same as the cost of a standard three-year degree in England.
But Aberdeen's announcement defied Scottish Government advice that universities here should show "restraint" and charge annual RUK fees closer to pound;6,000.
As other universities across Scotland prepared to set their fees this month, lecturers' representatives warned that their "worst fears" were becoming reality.
The University and College Union (UCU) Scotland said it was worried that despite the discount, "students will end up paying more to study in Scotland than even in England".
A spokeswoman added: "Our worst fears that some Scottish universities will ignore the minister and charge the highest possible fee are already coming to fruition. "
NUS Scotland said charging more than English institutions would be "entirely unjustifiable".
Robin Parker, NUS Scotland president, said:
"I am sure that students will come down hard on any principal who decides to make their degrees more expensive than a degree in England.
"If we see the cost of a degree above levels seen in England and weak fee- waivers and bursaries, then students from the rest of the UK will have every right to feel aggrieved and used by the Scottish sector."
Opposition MSPs said the English system was effectively being introduced in Scotland, against SNP policy.
Aberdeen University justified its controversial decision as a "very difficult" but "fair" choice prompted by changes to university funding instigated by Westminster.