Vice-chancellor of Ulster University Gerry McKenna has condemned top-up fees as "inherently discriminatory" and unfair on middle-income families.
Speaking at Limavady College of Further Education, Professor McKenna called for a graduate tax to solve the funding shortfall, with cash raised earmarked for higher education alone.
"A graduate tax has the virtue of simplicity, would raise large sums of money and has the ability to make education free from the point of access," he said.