The headquarters of Victoria's CFMEU have been raided as detectives probe kickback allegations.
Detectives from Taskforce Hawk, established to tackle criminal behaviour in the construction sector, executed warrants at six addresses on Monday morning as part of a investigation into information about "secret commissions", police said.
The force confirmed the CFMEU's headquarters, on Elizabeth Street in Melbourne's CBD, was one of the premises raided.
Five people, believed to be union organisers, were arrested and are being interviewed by police.
It comes after Victorian Premier Ben Carroll released the terms of reference for a royal commission into the state's construction sector, headed by former South Australian chief justice Chris Kourakis.
Under the terms of reference, Mr Kourakis will investigate the extent to which corruption, criminal conduct or serious misconduct has occurred on or surrounding any major public and civil infrastructure projects.
That includes any such activity undertaken or instigated by the CFMEU, construction companies and consortia, sub-contractors, labour-hire companies, contractors, suppliers or others.
The commission can also investigate whether Victoria's executive government or delivery authorities adequately followed their roles and responsibilities.
Barrister Geoffrey Watson's Rotting from the Top report claimed worksites became drug distribution hubs, killers were handed high-paying jobs and strippers performed for night crews after organised crime infiltrated the union.
He estimated Victorian government inaction caused $15 billion in blowouts on the state's $100 billion Big Build program.
The inquiry is due to produce a final report in August 2027 but Mr Carroll has revealed it could run longer.
"I think it will be an 18-month, potentially two-year process, but I don't want to pre-empt anything," Mr Carroll told Melbourne radio station 3AW on Monday morning.
The premier reiterated the commission will have the power to call him, former premiers, current ministers, business leaders and union bosses.
John Setka quit as head of the Victorian CFMEU in 2024 following a Nine investigation that alleged major Victorian and NSW construction projects had been infiltrated by underworld figures and bikies - allegations he denied.
The construction and general division of the union were placed into administration in mid-2024 in response to the allegations.
Earlier in August, Setka was arrested and charged for a third time over allegedly making threatening and harassing comments online about the union's administrators.
Australian Associated Press