Sessional or casual staff are the cogs who keep universities whirring. They run tutorials, deliver lectures, mark assignments and respond to queries from anxious students throughout the semester. But their work is precarious. They don't receive holiday or sick leave, often struggle to make ends meet and receive no pay during the midyear and summer breaks. According to the National Tertiary Education Union, the vast majority of casual staff are not being remunerated properly. The Victorian branch of the union is now investigating legal action against universities to ensure casual staff – which can make up to 60 per cent of an institution's workforce – are paid properly. "You don't have to work in a restaurant or a bar to be underpaid," the union's Victorian secretary, Colin Long, said.

"Universities have been prospering on the basis of the huge amount of unpaid work by casuals." In an attempt to document the scale of the problem, the union will soon launch an app for casual staff to log their paid and unpaid work. The union has already begun collecting timesheets from Monash University staff. Mr Kimberley is paid for 22 hours of weekly work at RMIT and the Australian Catholic University. But he said while his hourly rates take into account the preparation that goes into tutorials and lectures, it never covers the actual time he puts in.

He claims he spends twice as long marking students' work than he is paid for. "I have chosen to speak out because this needs to change," Mr Kimberley said. "I love teaching students, I love being a tutor, but it comes with a heavy price. I don't place blame on any one university, the whole sector is responsible for this." Once he completes his PhD, Mr Kimberley hopes to secure permanent work in academia. Michael Lazarus, who recently tutored at Monash University, said he was paid for four hours of weekly work, but worked another four.

"What they pay for is a very small fraction of the tasks that are expected in the job," the 27-year-old said. "It would be a superhuman task to do all that is expected in the time you are paid. It takes so much more time to plan the classes, provide detailed and useful feedback to students and reply to emails." Universities insist they pay staff for all the hours they work. They say pay rates are set out in workplace agreements that have been negotiated with, and approved by, the union. Australian Catholic University deputy vice-chancellor Dr Stephen Weller said his institution paid staff for the hours they worked. "The Enterprise Agreement gives academic staff the capacity to raise workload issues and have them escalated if not resolved. ACU has committed to work with the NTEU on a review of workloads in line with the changing needs of the organisation and of academic staff," Dr Weller said.