A union’s investigation into alleged underworld links has been attacked as a whitewash at the royal commission.

The union corruption royal commission has attacked a construction union internal inquiry into alleged death threats and underworld links as “a whitewash”.

The commission has also heard claims from the Construction, Forestry, Mining and Energy Union (CFMEU) that a building boss who accused the union of demanding corrupt payments had a history of underpaying workers and “phoenixing” failed companies.

Investigations continued on Tuesday into the CFMEU’s handling of death threat claims by whistleblower Brian Fitzpatrick.

Mr Fitzpatrick has alleged fellow union official Darren Greenfield told him: “I don’t care how many police you’ve got with you, I’m coming over there tomorrow and I’m going to kill you” after he complained about the CFMEU’s endorsement of labour hire and scaffolding companies linked to underworld figure George Alex.

The CFMEU commissioned an independent investigation which cleared it of any wrongdoing in relation to Mr Fitzpatrick, claims of bullying and favourable treatment of Mr Alex’s companies.

Barrister Tony Slevin investigated a series of claims made in a detailed letter from union official Andrew Quirk that the NSW CFMEU was “at risk of becoming a front for criminal figures”.

Mr Slevin reported in June that the complaints were “not substantiated”.

However counsel assisting the commission Jeremy Stoljar SC attacked the review on Tuesday during questioning of CFMEU legal officer Tom Roberts.

Mr Stoljar put to Mr Roberts that the Slevin report was “simply a whitewash” that “skates over” the claims of union links to Mr Alex raised by Mr Quirk.

It emerged that while Mr Roberts had made notes about Mr Slevin’s investigations, he had no written record of questions being asked about the key allegation – that union officials were associating with people with criminal connections.

Mr Roberts said he may not have made notes but believed the matter was asked about.

Mr Roberts also touched in his statement on Eoin O’Neill, the former manager of building company Lis-Con who accused the union of demanding corrupt payments and running a campaign to force his company out of Queensland.

Mr Roberts said a Queensland union official had told him Mr O’Neill had refused to pay workers’ superannuation and had a history of “phoenixing” – letting companies collapse without paying workers their owed entitlements.

Mr O’Neill is suing the union for defamation in separate proceedings.

The Royal Commission Trade Union Governance and Corruption continues in Sydney on Wednesday.