La Trobe University's review into potential staff wage theft is lacking transparency, the union says.
Staff were last week told in an email that the university had launched a project to review payment practices.
"We are not aware of any systemic issue with staff remuneration at La Trobe," the spokesperson said.
"Staff can raise questions about their payments at any time. We want to ensure that we conduct this survey and that systemic issues - if there are any - are disclosed quickly."
But La Trobe Casuals Network's convener Anastasia Kanjere said the university was trying to "bury" the review over the summer.
"It has been announced at a late date at the bottom of an email where a lot of people wouldn't have scrolled down," she said.
"It's also coming at a time where casual academic staff won't be checking their emails.
"There is no reason why it should close in January. It's a completely arbitrary date that the university chose. It's not good practice."
Ms Kanjere said the Casuals Network would support a review into systemic staff underpayment if it was done transparently.
"There has been no attempt to correspond with staff who have worked at La Trobe over the past six years, many of whom would be eligible for back payments," Ms Kanjere said.
"There has been no attempt to educate staff on the different forms of wage theft. There has been no transparency about how any claim would be evaluated.
"There has been no transparency about the power imbalance of a precariously-placed employee going to their employer with their concerns."
La Trobe's review came after the University of Melbourne started repaying staff about $6 million, following a dispute between the university and the National Tertiary Education Union.
Thirteen universities have also been referred to make submissions at the Senate inquiry into unlawful underpayment of employees' remuneration.
Ms Kanjere said wage theft was a systemic issue across the tertiary education sector.
"We're developing a submission to the Senate in the hope La Trobe will also be called," Ms Kanjere said.
"The University of Melbourne situation is proof that wage theft has occurred and it shows that casual staff are legally entitled to back payment.
"What La Trobe should be doing rather than pushing it under the carpet is partner with the union and the Casuals Network to genuinely find out the extent of the problem and look to rectify it.
"They shouldn't say they are not aware of systemic underpayment when we have been telling them about it. They are extremely aware."
The La Trobe spokesperson said the university was working closely with the NTEU and auditors in the review process.
Ms Kanjere said the Casuals Network would be there to support staff.