The federal government has ordered an investigation after the ABC uncovered allegations that outlaw bikies threatened a CFMEU delegate during the union's dispute with a construction company on a major taxpayer-funded project in Brisbane.

The ABC has sourced multiple insider accounts alleging senior Comancheros bikies are claiming to be linked with Host Group, a security provider employed by builder BMD on the $300 million Centenary Bridge upgrade.

Underworld and security industry sources said those bikies included former Comancheros national president Bemir "Benji" Saracevic and his business partner Krstomir "KB" Bjelogrlic.

The Melbourne-based bikies, who appeared in Queensland wearing "bumbags and Balenciaga t-shirts", held themselves out to the CFMEU and others as "directors" of Host with a financial interest in the company, the sources said.

However, ASIC records show they are not listed as directors and the company has denied any involvement with them.

The bridge project in Brisbane's west has become a flashpoint for a national CFMEU campaign against BMD, with police repeatedly called amid union clashes with security during site blockades in May.

CFMEU members picketed the site and blocked trucks and other workers from entry, while the union, which has been pushing for a workplace agreement with BMD, claimed its officials were blocked from safety inspections by Host staff.

Multiple sources told the ABC that in early June, Saracevic and Mr Bjelogrlic allegedly confronted a CFMEU delegate near the site after he had a verbal altercation with a Host representative.

The bikies allegedly threatened to burn down his house with his family inside, the sources said.

Murray Watt, the Federal Minister for Employment and Workplace Relations, said these were "yet more serious allegations about the infiltration of organised crime within the construction industry".

"It doesn't matter whether it's the CFMEU or employers, there is no place for bikies seeking to legitimise their criminal activity through taxpayer-funded infrastructure projects," he said.

"As soon as I was made aware of these allegations (raised by the ABC) I requested urgent advice from my department and am taking action today to refer to the allegations to the Fair Work Ombudsman for investigation."

The federal government is set to pass laws forcing an independent administrator on the CFMEU and the removal of top officials, after referring allegations of bikie infiltration of the union to the FWO and Australian Federal Police.

CFMEU 'not gangsters'

But sources outside the CFMEU said in this case, the union had become the target of bikie intimidation.

"The CFMEU think they're gangsters. They're not," one underworld source said.

The source, who asked not to be named because of concerns for his safety, alleged that Comancheros bikies were claiming a connection with Host to engage in "union busting".

They allegedly include Saracevic, Mr Bjelogrlic and the club's national president Allan Meehan.

A security source, also speaking on condition of anonymity out of fear of reprisals, said: "There's a lot of heavy people involved."

"They're just ruthless c***s, put it that way. They don't give a f***, man."

Saracevic is a Bosnian-born house painter who made headlines when he arrived in a $700,000 Lamborghini Aventador at a Comanchero national rally in Melbourne in 2022.

Last year he briefly replaced Meehan as national president of the Comancheros.

In 2016, a Victorian judge sentenced Saracevic to four-and-a-half-years jail as the ringleader of Comancheros "thugs" who tried to extract debts from three men using blackmail, threats and violence.

Saracevic, who also pleaded guilty to unlawful possession of a loaded semi-automatic pistol, had two other bikies tape a bullet to one victim's front door.

Mr Bjelogrlic is a former owner of a gym chain in Melbourne, which was the subject of repeated police raids and drive-by shootings over its Comanchero links.

A Host spokesman has denied the bikies' claims of a connection with the company.

He said the bikies "you referenced have no role whatsoever with Host".

"Any suggestion otherwise is utterly untrue and is consistent with ongoing smear campaigns by those who have recently been exposed for their own ethical, compliance and legal failings," he said.

"We are aware of recent revelations of the CFMEU having been infiltrated by alleged criminal syndicates. By comparison, we have had a constructive working relationship with the Australian Workers Union (AWU) on our building sites for many years."

Queensland police said there had been no report of the alleged threat.

The CFMEU declined to comment on the incident.

'No place for criminality'

Saracevic did not respond to calls and texts.

Mr Bjelogrlic hung up on the ABC and did not respond to questions. 

A BMD spokeswoman said the company had "received assurances that the individuals you have named are not employed by or connected to the security provider contracted to provide security on the project".

A Transport and Main Roads Department spokeswoman said it had received the same assurances.

Queensland Transport Minister Bart Mellish said there was "no place for criminality on any worksite".

"If anyone has any information regarding criminality on worksites, I strongly encourage them to report it to authorities."

The Queensland government has invested $159 million in the project, along with $139 million from the federal government.

BMD's other taxpayer-funded contracts include the Olympic Games athletes' village in Brisbane, the Camden water treatment plant in Victoria, and upgrades of air force bases in Queensland and Victoria.