Too many lecturers are struggling to make ends meet on casual contracts, says the academics' union UCU.
The University and College Union questioned more than 2,500 of its members on casual employment contracts in further and higher education.
Of these, 42% said they had problems with household bills, 35% with rent or mortgage and 21% struggled to buy food.
But a university employers' body said the study was flawed as not all the contracts would count as casual.
The union's study, Making ends meet: The human cost of casualisation in education, was carried out between January and April this year.
About 2,550 staff on casual contracts at UK universities and colleges responded - 71% were from the higher education sector, the rest from further education.
About a quarter said they were on zero-hours contracts, 45% were on fixed-term contracts and 32% were paid by the hour.
They included lecturers, tutors, trainers, researchers and postgraduate teachers.
The figures varied between sectors, with 55% of the higher education staff on fixed-term contracts and 32% of the further education staff on zero-hours contracts.
Overall, 47% worked up to 30 hours a week and 33% earned less than £1,000 a month, the survey found. .
About one in 10 could not say how many hours they worked in a week because their employment was so irregular, says the report.
Many said they worked long hours because of worries about where their next job was coming from or because they knew they would not be paid over the holidays.
Some said their hours were being cut to make way for cheaper staff.
UCU general secretary Sally Hunt described some of the employment contracts in the study as "exploitative" and leaving people "unable to plan their lives month by month or even week by week".
"Ministers and employers must stop trying to defend these practices as flexible. People who want security and a proper contract should be able to get one.
"The high levels of casualisation in further and higher education would shock many students and parents and expose the harsh reality of life in modern universities and colleges."
The union says the most recent official figures show more than a third (36%) of academics in higher education were on fixed-term or temporary contracts in 2013.
But the University and Colleges Employers Association (UCEA) disputed the union's definition of fixed-term employment as casual work, pointing out that fixed-term contracts were primarily used for researchers on externally funded projects, lasting three or four years.
A spokesman said numbers of permanent contracts had risen in recent years and, once research contracts were excluded, the proportion of work done by casual staff was more like 3%.
"Higher education institutions cannot simply provide full-time or open-ended employment to everyone who wants it. Like all employers they will always have variable and temporary needs."
The spokesman said specialist lecturers, who combined teaching with other employment in their profession, often preferred flexible contracts.
The Association of Colleges (AoC) said further education had always needed a flexible workforce and employed people on different types of contracts according to need.
"These needs include the levels of demand for some courses, covering staff absences and delivering short courses," said Marc Whitworth, the AoC's employment and policy director.
Mr Whitworth said the UCU's conclusions were "concerning" but "not representative of the discussions we have had with our college members".
A report on casual and hourly paid staff in higher education is due to be published next month after an eight-month inquiry by a joint working group of unions and employers.