The Union of Students in Ireland (USI) fears library fines are being used as a "money-maker" after it was revealed almost €500,000 is paid by students each year in Ireland's biggest colleges.
The figures across Ireland's nine largest third level colleges show that, over a five-and-a-half-year period, €2,786,930 was paid in library fines thanks to overdue books.
The figures, revealed under the Freedom of Information Act, included Ireland's seven universities - Trinity College, Maynooth University, University College Dublin (UCD), Dublin City University, University of Limerick, University College Cork, and NUI Galway.
Dublin Institute of Technology (DIT) and Waterford Institute of Technology were also included.
The largest amount received was at Trinity College, with €112,111 paid to the university each year.
This works out at around €597,925 over the period from September 2010 to January 2016.
It was also more than double the average that was owed to the college - €53,902.
Speaking to the Herald, USI President Annie Hoey called for a cap on fines to be introduced across the board for college libraries and said that she would like to know if the money is used to improve facilities within the library.
"Library fines as an overall concept are nothing new - you get fines from your local library," Ms Hoey said.
"What we would be concerned about is when a fine moves from being reprimanding for late books and it turns into a substantial cost, which puts a student at a severe disadvantage.
"If it becomes quite apparent that library fines are being simply used as a money-making mechanism, obviously we would have concerns about that.
"I haven't looked at all of them and how much each of them charges and what their different breakdowns are," she added.
DIT, which received €312,694, imposes a maximum fine of €30 per item taken from the library - with a maximum of six books permitted at any one time.
However, UCD, which took in €343,673 in the same period, has a maximum fine of €50.
It was unclear whether any maximum sanctions applied to some of the other colleges in question.
However, a number of colleges do not allow students to graduate until they have settled any overdue payments owed to the library.
Meanwhile, the top colleges are also losing out on some income, with students and members of staff guilty of not paying fines totalling €1,204,291 over the same period.