Dozens of people are now infected with COVID-19 in a cluster linked to a protest outside the construction union's Melbourne headquarters two weeks ago, according to the CFMEU.
The CFMEU's Victorian construction secretary John Setka said seven officials and staff had been confirmed to have contracted the virus and "close to 40" family members and close contacts were now infected.
Those numbers and the link to the protest have not yet been confirmed by the health department.
Hundreds of people protesting against mandatory vaccinations in the construction industry gathered outside the CFMEU on September 20, and clashed with union officials.
CFMEU secretary John Setka said the infection had spread to 14 members of one official's family, and at least 12 cases linked to the protest were in children under 10.
"We've got a case of a four-month-old toddler who's got it, young children, grandparents, it is just absolutely terrible," he told ABC News Breakfast.
"My understanding is some of them are seriously unwell, I don't think they're on a ventilator but they're not really travelling that well."
Mr Setka, who had to undergo quarantine after being deemed a close contact, said he had visited his elderly parents to conduct a welfare check in the days after the protest and before the first linked case was detected.
"Until I got my [test] results I was absolutely beside myself — they're 86 and 87 — wondering if I'd given them COVID," he said.
Mr Setka said no union member had been expelled over the illegal protest, but CFMEU officials had identified a number of members in vision taken on the day.
He said union members were seen throwing projectiles and kicking in windows, and they would likely be called before the union's executive to explain why they should not be expelled.
"We don't need people like that in the building industry, it's a dangerous industry and if people want to behave in that manner they can go and work somewhere else," he said.
Despite the union's condemnation of the protesters, Mr Setka said the CFMEU would represent workers who lost their jobs because they refused to comply with the industry's vaccination mandate.
Mr Setka said some people in the industry had genuine reservations about mandatory vaccination, and the union would provide them with legal advice through law firm Maurice Blackburn should they lose their jobs.
"Whether we agree with it or not, we have to respect that genuine fear," he said.
