A union at the centre of a construction corruption scandal denies offering whistleblower Brian Fitzpatrick a bribe to keep quiet and is dubious of claims he received death threats.

Mr Fitzpatrick, who worked with the Construction, Forestry, Mining and Energy Union (CFMEU) for 25 years said he received death threats and was offered a $300,000 bribe, sourced from union members’ money, to leave quietly after raising concerns about links between union officials and crime figure George Alex.

Mr Alex was awarded a lucrative contract at Sydney’s Barangaroo South project after intervention by allegedly corrupt CFMEU officials, according to media reports.

But CFMEU NSW secretary Brian Parker says no money was offered to Mr Fitzpatrick and that he has no relationship with Mr Alex.

“The CFMEU does not employ gangsters or members of motorcycle gangs and our office is not infiltrated by criminals,” he said in a statement.

“We are deeply concerned about any such activity in the industry.”

He added that there were “issues around the employment of Mr Fitzpatrick and his suitability of continuing to work for the union”.

“He was the subject of complaints from other staff in our organisation,” Mr Parker added.

“I am not at liberty to discuss these complaints.”

Mr Parker said police and the CFMEU had investigated Mr Fitzpatrick’s allegations to the union that he had received death threats.

“The union could not form a conclusion that Mr Fitzpatrick’s allegations were true,” Mr Parker said.

The federal government wants the allegations investigated as part of a wider royal commission into unions, but the CFMEU and Australia Council of Trade Unions have rejected the call.