Construction, Forestry, Mining and Energy Union state secretary Andrew Ferguson told police yesterday about threats made to his staff by individuals from the company.
The CFMEU office was gutted by fire on Thursday night after a stolen Mazda 626, filled with drums of petrol, was driven through the foyer and set alight about 10.30pm.
Union officials told detectives they met with the construction company earlier in the day about a dispute involving migrant workers.
Mr Ferguson, who would not reveal the name of the company, yesterday described the ram-raid as un-Australian.
"We're involved in a dispute with a contractor who has underpaid migrant workers," he said.
"There have been some menacing remarks towards one of our officials."
The ram-raid was captured on CCTV cameras.
Mr Ferguson said that the attack would have a major impact on local community groups and a Buddhist festival planned to be held at the CFMEU headquarters over the weekend will have be relocated.
The ground floor of the building was extensively damage, while upper levels suffered smoke damage.
Mr Ferguson said smoke alarms and the office sprinkler system had saved the building from destruction.
A church group was using the office an hour before the attack.
