Western Sydney University has warned staff it will cut casual workloads next semester as it faces mounting financial shortfalls over the next three years due to the coronavirus pandemic.

It comes amid mounting concern about casual workforces across the state's universities, with Sydney University slashing up to 30 per cent of its arts courses and one-third of casuals at the University of NSW reporting they've lost work.

"This is not a one-off hit," WSU Vice-Chancellor Barney Glover told staff via video link on Thursday. "The challenge is bigger in 2021 [and 2022] than it is in 2020."

The university has flagged a $90 million shortfall in 2020, which could grow to between $120 and $130 million in 2021 and 2022 as travel restrictions remain in place and anticipated growth fails to materialise.