The STUC has launched a support and advice service for students forced to take jobs to pay their way through university.
Unionlink is a pilot project at this stage, confined to Edinburgh University students, but will be extended to other colleges and universities if it proves successful.
Research carried out for the STUC among 400 working students in four Scottish universities shows that students are on average working 15.5 hours a week, and that 80 per cent are doing so just to pay the bills.
Nearly 70 per cent report a level of tiredness which affects their studies, with 34 per cent saying this is always or often the case. Students expect to be nearly pound;10,000 in debt by the time they finish their studies.
David Moxham, STUC assistant secretary, said it did not oppose "sensible working" by students but added: "It is clear that a number face severe stress in managing their working lives with full-time study."
Mr Moxham said students were a source of cheap and flexible labour for employers but "all too often their working experience is poor and sometimes illegal".
A Unionlink card will secure employment advice, legal support and campaigning opportunities through the unions on matters relating to work-study balance.
The STUC research, carried out by academics from Stirling University, showed that the average pay for working students is pound;5.49 an hour, 10 per cent above the adult minimum wage. Around a third of students are on or below the minimum wage.
The survey came across five people who were paid illegally in terms of the wage rate relevant to their age.
The value of students to employers is underlined by their working conditions - 60 per cent do not receive sick pay, 31 per cent do not receive paid holidays and 34 per cent are paid in cash. Nearly a quarter, 24 per cent, do not have a formal contract of employment.