One of Australia's largest universities underpaid almost 10,000 casual staff members by more than $7.5 million over seven years.

The University of Queensland has sent an email to staff apologising for the mistake, which it said related "to the minimum hours of engagement for casual academic and casual professional staff and the use of a different pay rate for casual academic staff with a relevant PhD".

The email from Vice-Chancellor Professor Deborah Terry AC said the period spanned from January 2017 to December 2023, and the total amount owed to the 9,743 affected staff was $7.88 million. 

That figure does not include any interest or superannuation.

She said the median amount owed was $243. 

The underpayment was discovered in a pay review initiated in October 2021.

National Tertiary Education Union (NTEU) Queensland secretary Michael McNally said the scale of the underpayment was "staggering". 

He said the incident was the latest in a series of underpayment problems plaguing the sector, which he said has eclipsed $180 million nationwide.

"Unfortunately, the sector seems wedded to this model," he said. 

"The simple answer is to have less casual staff — to have less of a dependence on casual staff that really isn't casual.

"The university is clearly struggling to pay them properly, which boggles the mind given the size of UQ; I mean, it's a two-and-a-half billion-dollar organisation."

In a statement, the university said "work to further improve [its] systems and processes is ongoing".

"The Office of the Fair Work Ombudsman and relevant statutory authorities have been advised," it said. 

The vice-chancellor's email said a repayment scheme, which will include superannuation and interest, would begin on June 14.