Embattled Victorian Premier Jacinta Allan is facing a motion of no confidence after a difficult week of internal pressure and scrutiny over alleged corruption within the CFMEU. 

Opposition Leader Jess Wilson is due to give notice to state parliament's lower house on Thursday to move a motion of no confidence in the premier and her ministers.

Only one motion of no confidence can be moved per four-year term and it can trigger the dissolution of parliament if passed, well before the scheduled state election on November 28. 

Wilson cited record crime, soaring net debt, major project cost blowouts and delays, and the failed 2026 Commonwealth Games. 

'Victoria needs a fresh start and that begins with changing the government and changing the premier,' the state Liberal leader said.

The earliest the motion can be debated and voted on under the terms of Victoria's Constitution Act is July 28, when state parliament returns following a six-week break. 

The bid to oust Allan is doomed to fail, with Labor holding an overwhelming majority in the lower house.

But it comes during a challenging week for the premier, who endured tough questions about her handling of the CFMEU during an appearance on ABC's 7.30 on Tuesday.

A Queensland-based inquiry in February estimated that criminal activity within the construction union may have cost Victorians up to $15billion.

The report detailed a series of explosive allegations tied to major infrastructure projects, including claims that strippers were recruited and paid to perform on taxpayer-funded 'Big Build' sites.

It also alleged construction sites were used as hubs for drug distribution linked to bikie gangs, while convicted criminals, including violent offenders, were allegedly appointed to lucrative union positions. 

Despite the findings, Allan said the $15billion estimate was 'in dispute' when challenged by ABC host Sarah Ferguson. 

'We have absolutely acted quickly and strongly,' the premier said, pointing to expanded police powers to investigate organised crime links within the sector.

In her previous role as infrastructure minister under former premier Dan Andrews, Ms Allan oversaw Victoria's 'Big Build' program - the same projects at the centre of the allegations. 

Asked repeatedly by Ferguson whether she accepted the figure or could provide an alternative, Allan declined to give an estimate. 

'The work is being done now to go after this criminal behaviour but also to change the culture,' she said.

Allan said her government had introduced enforcement measures and strengthened authorities' response to alleged criminal infiltration.

'We have absolutely acted quickly and strongly,' she told Ferguson.

She added that police had been granted additional powers to investigate suspected links between bikie groups and elements within the CFMEU.

On the same day, Allan also faced internal pressure over Labor's tanking poll numbers.

However, a speculated leadership challenge did not emerge when the party caucus met on Tuesday after her main rival, Deputy Premier Ben Carroll, ruled it out. 

The meeting was seen as the last chance for at least six weeks to challenge her leadership, unless a special sitting is called during the mid-winter break. 

Nine newspapers' latest Victorian Resolve surveys this week showed primary support for Labor falling to 26 per cent, level with Wilson's coalition.

Support for One Nation was up three percentage points to 24 per cent.