The national construction watchdog is investigating a Melbourne developer after two union workers were allegedly attacked while visiting a job site.
The officials, from the Victorian branch of the CFMMEU, were allegedly set upon at a construction site on Toorak Road in Hawthorn East on Tuesday.
The head of the union's construction division John Setka said the duo were on the footpath filling out paperwork to enter the site when they were "brutally attacked."
"Of course, emotions are running high within the construction industry, as these young officials were simply doing their job when met with an organised assault by a group of cowards," he said in a statement on Wednesday.
"The attack was so violent, with one of the officials hit across the head with a lump of timber and knocked unconscious. We are all disgusted."
Mr Setka said the officials went to inspect the site after concerns were raised about the developer, named in media outlets as Raman Shaqiri.
Mr Shaqiri was fined alongside developer Stefce Kutlesovski after they knocked down the 159-year-old Corkman hotel in Carlton without permission in October 2016.
"These are the developers that pulled down the Corkman hotel and dumped all that asbestos in Caroline Springs in that residential area," Mr Sekta told 3AW.
"There have been residents ringing up and complaining that they block off the traffic, they set up concrete pumps with no permit, residents can't walk past the footpath.
"So not only construction workers are in danger, the general public is in danger."
A lawyer for Mr Shaqiri confirmed he is involved in the building works, but added the development "is not in any way related to the developer ... of the Carlton Inn site".
The statement from Francke Lawyers added that two people saying they were union officials visited the building site.
"They were asked several times why they were seeking entry ... they would respond with one word 'ARREO'," the statement added, referring to the abbreviation for authorised representatives of registered employee organisations.
The statement said the two people refused to respond when asked to produce documents and they were denied entry.
"They then became physically aggressive and two staff members of the builder acted defensively. No weapons were involved," the statement claimed.
The Australian Building and Construction Commission and police are investigating the allegations.
CFMMEU members gathered at the construction site on Wednesday morning to protest the attack, drawing a much larger crowd than anticipated.
Victoria Police said the organiser has been fined $1652 for breaching COVID-19 rules. No further fines will be given in relation to the protest.
Police are investigating the alleged assault.