The tertiary education union says the Australian National University has a backpay bill likely worth hundreds of thousands of dollars after paying some casual academics at the incorrect rate since at least the start of this year.
The ANU is scrambling to figure out how many casual academics working within the Fenner School of Environment and Society are affected by the error after being alerted to the issue by the National Tertiary Education Union.
"The university is reviewing a significant amount of payroll data, including superannuation, as quickly as possible and is aiming to make adjustment payments to affected staff," a spokesman said.
"We expect to have fully resolved this issue in the next six weeks and all affected staff are being contacted directly."
One casual academic, who spoke to Fairfax Media anonymously, said he realised his pay was incorrect after speaking with colleagues and finding out they were paid different rates.
The PhD student and tutor said he believed whatever he was owed for his two semesters worked would be in "the low thousands".
He suggested the underpayment was indicative of a broader problem and said he had not been contacted by the university.
"There's plenty of money floating around because students are paying through the nose to do their degrees, but it seems to be the casual staff which are mostly made up of PhD students - perhaps ... because they don't have the time to deal with this sort of thing - being taken advantage of," he said.
"I think beyond Fenner School it's a fairly frequent occurrence that whether you are technically underpaid you're doing work that you're not being paid for as a tutor generally."
NTEU ACT organiser Lachlan Clohesy said the payout could potentially be one of the ACT's largest, adding each academic involved was believed to be owed several thousand dollars.
"Let's be clear - this is not a sudden bonus or windfall for these workers," he said.
"It is the returning of tens, perhaps hundreds of thousands of dollars that they should have been paid in the first place."
Union ACT secretary Rachel Bahl said the disappointment was "part of a much broader problem - the casualisation of academia".
"Casual workers are already propping up the higher education system in this country," she said.
"Our workplace laws need to change to protect casual staff from exploitation, and encourage the creation of secure jobs."