The ANU Union, which also oversees the ANU Bar, begun legal action after it failed to negotiate with the ANU where it would be relocated once demolition of the square began.

The stoush is the latest development in a project that has pitted the university against Gods Cafe owner Jaye Min, who argued in court the ANU sought to end his lease illegally.

Mr Min won a reprieve last week when a Canberra court granted the cafe a stay of execution until a judge could properly hear a dispute about the lease.

In a statement earlier this week, the ANU Union said the legal action meant the ANU will be unable to evict the union from its current offices, with the two groups to meet for a court hearing in mid-October.

An ANU spokesperson said on Tuesday they couldn't comment on matters before the courts.

"ANU negotiated in good faith with all parties, including offering space in the Pop-Up Village and nearby," the spokesperson said.

"We have been discussing the project with the ANU community since December 2014."

ANU Union chair Tom Lindenmayer said they'd receive a lot of support from the student body and broader Canberra community over the legal action,

"Many students have a strong attachment to the ANU Bar, and are supporting us as we continue to negotiate with the University," Mr Lindenmayer said.

"Legally, the matter is exceptionally complex, given the long history between the two parties, and the complexity about the ownership of the building."

"The ANU Union is continuing confidential negotiations with the University at this stage, so it would not be appropriate to comment on the specifics."

Mr Lindenmayer said the union was not against the redevelopment, believing it would benefit the ANU community, but it "should not come at the cost of the ANU Union".

The Union Court redevelopment is set to cost $220 million, adding more classrooms, bars, accommodation and event spaces to the university.