Mr Fitzpatrick told the royal commission's hearing on Tuesday that he received the death threat at 5.05pm on March 27 last year after he tried to stop his union dealing with Sydney crime figure George Alex.

Fairfax Media revealed the alleged death threat in January. Counsel assisting the royal commission, Jeremy Stoljar, said the triple-0 phone call was a "telling piece" of new evidence that "strongly corroborates Mr Fitzpatrick's account of events".

Mr Fitzpatrick said the caller screamed with "absolute rage" words to the effect of: "You have gone too far this time you fat c---. You're dead. ... I'm coming over there tomorrow and I'm going to kill you."

A recording of a triple-0 phone call that CFMEU industrial officer Radhika Raju and Mr Fitzpatrick made at 5.20pm was played during the hearing in Sydney.

In it, Ms Raju says Mr Fitzpatrick was told he would be killed the next day.

Another union employee, Peter Thomas, told the inquiry Mr Fitzpatrick "appeared very unsettled" after he received the alleged call.

Mr Stoljar said: "Indeed it is clear from the recording that neither Ms Raju nor Mr Fitzpatrick had the slightest doubt that a death threat had been made."

Mr Fitzpatrick assumed the call was from a union member who had previously made threats against him but soon discovered it was from another colleague, Darren Greenfield. Mr Greenfield has admitted to making an angry phone call but denied any death threats.

Mr Fitzpatrick said when police arrived in response to the triple-0 call, he told them it was a "false alarm" because the death threat was made by a "comrade" and not the person he originally thought.

Outside the royal commission, CFMEU national secretary Dave Noonan said these were "hardly the actions of a person who is concerned for his life".

The royal commission heard Mr Greenfield had close dealings with Mr Alex, whose labour hire companies received preferential treatment. Mr Fitzpatrick said Mr Alex would often meet in the CFMEU office with NSW secretary Brian "Sparkles" Parker, who had refused to intervene in his dispute with Mr Greenfield.

In sworn evidence, Mr Fitzpatrick said he discovered Mr Alex was associated with companies that were behind in paying workers their superannuation and redundancy entitlements. The union said it recovered more than $900,000 from Mr Alex's companies between mid-2012 and early 2014.

Mr Fitzpatrick claimed union officials wanted to "get rid" of him "because I wouldn't drop off the George Alex business".

But Mr Parker has said Mr Fitzpatrick left the job for reasons "completely unrelated" to his allegations.

In Victoria, police are investigating allegations that Hells Angels associates hired to intervene in a building industry dispute threatened to bash two building contractors, including a man who days before had given royal commission evidence about organised crime in the sector.

The anti-bikie Echo Taskforce is overseeing an investigation into an incident on Saturday, in which two men allegedly bearing weapons threatened to bash Andrew Zaf and a second contractor in connection with a disputed debt.

The allegations are corroborated by a witness statement and video recordings, which show a Hells Angels-owned tow truck arriving at the site and heated discussions between Mr Zaf, a witness and employees of the building company who hired the bikie-owned tow truck.

The revelations have no connection to the building union or Mr Zaf's claims to the royal commission last week about alleged corruption involving its officials.