The acting City of Perth chief executive has taken sudden personal leave, citing an unsafe work environment as the reason.

The ABC understands councillors were informed of the latest unrest at the City of Perth in an internal message from Lord Mayor Lisa Scaffidi late yesterday afternoon.

Robert Mianich has only been acting in the role for a matter of days since CEO Martin Mileham went on sudden indefinite stress leave to deal with health issues he claims were caused by Council allegedly breaching terms of his employment contract.

Mr Mileham told councillors the alleged contract breach had impacted on his and his family's wellbeing, and made him feel "unsafe in the workplace".

A spokesman for the City of Perth confirmed on Monday night that Mr Mianich had taken "personal leave and would return on Tuesday 6 March".

Mr Mianich with Lord Mayor Lisa Scaffidi after Martin Mileham took indefinite personal leave. ( ABC News )

The spokesman refused to comment further.

The ABC understands Mrs Scaffidi emailed councillors late on Monday, saying Mr Mianich had texted her to inform her he would not be back at work for a week because the environment was "not safe at present".

Mrs Scaffidi said she could not say whether the City of Perth was an unsafe workplace until more facts were before her.

"It's not good to see your CEO that's highly regarded go on stress leave, and then the one that's appointed in the acting capacity also go on stress leave," she said.

"This is all just happening around us and it's very, very concerning."

Move to change CEO policy

Mr Mileham has been City of Perth chief executive since 2016, although his appointment was not supported by a number of councillors, who felt he was close to Mrs Scaffidi.

City of Perth CEO Martin Mileham left soon after an annual performance review. ( ABC News: Irena Ceranic )

Last week he announced Mr Mianich would take on the role while he dealt with his health matters, and urged the council to cease actions that put his and his staff's wellbeing at risk.

The ABC revealed on Monday that a group of councillors was planning to oust Mr Mianich at a special council meeting to be held on Tuesday.

It is understood the group were unhappy with Mr Mileham's decision to appoint Mr Mianich, who was previously the City's corporate services director.

Under existing City of Perth policy, the incumbent CEO has the power to appoint someone to act in the role.

The ABC understands a group of councillors had planned to force a change in that policy after calling the Tuesday meeting.

It is understood that change has the backing of most councillors, and would lead to the immediate appointment of another member of the City's executive leadership to take on the role of acting CEO.

It is not clear who that person would be.

Scaffidi hits out at move

Mrs Scaffidi criticised the push to call the special meeting, describing it as "entirely inappropriate".

Mrs Scaffidi says she is concerned by developments at the council. ( ABC News: Eliza Laschon )

But she said while she did not support the meeting, she was unable to stop it.

"It looks like the intention is to remove the acting CEO and appoint another director into that position … it's under a change in policy," the Lord Mayor said.

Last week, Mrs Scaffidi said Mr Mileham had gone on sick leave after he discovered legal firm Freehills had been appointed to advise about his conduct.

The firm found there was no conduct of Mr Mileham's that required explanation.

Mr Mileham has warned councillors he reserves his rights in relation to the matter, and has called on the Council to cease and desist actions that continue to put his and his staff's wellbeing at risk.

Local Government Minister David Templeman said he was now expecting to receive a report on a departmental investigation into issues at the City of Perth in the next 48 hours.

He said he also hoped to meet with the Council tomorrow.