The union corruption inquiry has heard private details of construction workers were leaked to a union to use in a war with a building company.

A former union official has told an inquiry the construction union used confidential information from a superannuation fund to stir up trouble with employees at a company with whom it was at war.

Former Construction, Forestry, Mining and Energy Union (CFMEU) official Brian Fitzpatrick told the Royal Commission into Union Governance and Corruption that the union obtained personal details of employees of construction firm Lis-Con from Cbus, the building industry superannuation fund.

Mr Fitzpatrick, a former coordinator at the union, told the commission that CFMEU NSW secretary Brian Parker directed him to contact Cbus to ask for information about Lis-Con employees.

In a statement to the commission, Mr Fitzpatrick said he obtained some information and later Mr Parker obtained details of all of Lis-Con’s workforce.

He said Mr Parker obtained addresses and telephone numbers for the Lis-Con employees and Mr Fitzpatrick then rang three of them, pretending to be a Cbus employee and warning them that Lis-Con was behind in super payments.

“Within a couple of days, (Lis-Con manager Eoin) O’Neill called Parker and wanted to set up a meeting to talk about peace,” Mr Fitzpatrick said.

Mr O’Neill appeared before the commission on Tuesday and gave evidence that his workers had complained about “stupid phone calls” where they were rung by people claiming to be from Cbus who hung up when asked their names.

“They were rough and ignorant, that’s why our people were pretty unsure that it was Cbus,” Mr O’Neill said.

Earlier on Tuesday Mr Fitzpatrick gave evidence of a death threat he received from a fellow union official after he complained about favourable treatment given to a labour hire company with underworld links.

Mr Fitzpatrick said he received a call in March, 2013, where the enraged caller said: “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!”

Subsequent checks revealed the call came from the mobile phone of CFMEU organiser Darren Greenfield.

The commission heard that when Mr Fitzpatrick told his boss, Mr Parker, about the threat, Mr Parker’s alleged response was “Well what can I do if two people don’t like each other?”.

Mr Fitzpatrick claimed he was subsequently victimised because he had called police about the death threat and because he continued to complain about the favourable treatment of the labour hire firm owned by underworld-linked figure George Alex.

He said he was forced out of the union – taking early retirement in September 2013 – but was not worried by threats of being sacked because he knew about the superannuation information illegally obtained from Cbus.

In a statement released on Tuesday, Cbus said it was “gravely concerned” about the allegations and was investigating any possible breaches.

Cbus also said its debt collectors had pursued Lis-Con over unpaid workers’ super entitlements “on multiple occasions dating back to 2004”.

CFMEU national construction secretary Dave Noonan, in a statement, said the commission’s rules that allowed evidence to be advanced without immediate cross-examination “allowed questionable claims to be put forward without challenge”.