Scottish graduates are paying up to £225 to take part in ceremonies, according to the National Union of Students.
The NUS said most Scottish universities were charging specific graduation ceremony fees.
Some are also charging students to simply graduate – even if they do not take part in the ceremony.
But the organisation which represents universities said fees are often much lower than the NUS findings.
The data was obtained by Freedom of Information requests by NUS Scotland to Scottish colleges and universities.
The union said the replies showed a mixed approach to charging, with specific graduation fees in place at 70% of universities and 16% of colleges.
It added that the costs varied, from £80 to £225.
All universities require library fines to be paid in full before students can graduate.
Many institutions also require students to externally purchase academic dress and robes, with some institutions receiving commission on each hire.
NUS Scotland President Liam McCabe described the fees as a “stealth tax” on student success.
“A student’s graduation should be one of the most memorable days of their life as they celebrate their hard-earned achievements,” he said.
“However, NUS Scotland’s FOI has revealed many institutions are putting a price on success through disgraceful graduation fees, effectively taxing students by stealth.
“Not only do many institutions – particularly universities – demand payment to graduate in the first place, they also require their students to hire and wear expensive academic robes from third party providers. Stunningly, some institutions even get a kick back on these transactions, receiving commission from the involved companies.”
He added: “We would appeal to all institutions across the country to reflect on their graduation fee policies and the impact they have on their least affluent students. Institutions must ensure that, in future, their graduations are free and accessible to all those who have earned the right to celebrate their academic successes.”
‘Rite of passage’
Universities Scotland – which represents the common interests of universities – said institutions took different approaches to their graduation ceremonies but that it had found the costs involved to often be much lower than the NUS Scotland findings.
A spokeswoman said: “In some cases the ceremony is free to the student and guests. In others, the modest fee also means membership to university graduates’ associations or the equivalent over the longer-term.
“Many institutions make hardship or discretionary funds available to students who would struggle to meet these costs. Arguably, a modest contribution from students, where they have the means to do so, and discretionary funds in place for those students who do not, is a fair way to cover this rite of passage which is valued by the graduates and their families.”
The spokeswoman added: “Universities ensure the ceremonies are inclusive, often streaming them free online, with sign language interpreters for accessibility.
“The degree itself needs to be protected against counterfeiting and fraud, using sophisticated printing technologies. Unfortunately, all of this comes at a cost. If universities made this completely free to every graduating student it would ultimately mean it is funded by taxpayers and would mean less invested in students’ higher education whilst at university.”