Four union workers have tested positive so far, with other staff members being forced into 14 days of self-isolation.
John Setka, secretary of the Construction, Forestry, Maritime, Mining and Energy Union (CFMEU) for Victoria and Tasmania said the outbreak was caused by the protesters' "disgusting" behaviour.
Reckless behaviour slammed
Mr Setka issued a statement condemning the people that protested.
“This outbreak caused by the disgusting behaviour of selfish and reckless people with no regard to the wellbeing of the thousands of construction workers or their families will not deter our commitment to getting construction back open and all our members back to work," he said.
"The declaration of the CFMEU head office as a tier one exposure site means the building at 540 Elizabeth Street, Melbourne has forced union staff and officials into two weeks isolation.
“The union has worked tirelessly over the past 18 months to keep construction open and members working safely while so many other industries were shut and thousands out of work, many for well over a year," Mr Setka continued.
“The shutdown of the industry last week was devastating for 300,000 plus construction workers and the lack of prior consultation from the CHO even more frustrating.
“Construction workers not being able to work and earn an income to put food on the table and pay mortgages puts enormous stress on families."
Protests a reaction to mandatory Covid-vaccinations
The protests initially began in retaliation to mandatory Covid-19 vaccinations for the construction sector being introduced, and building site tea rooms closing due to Covid restrictions.
Last Wednesday's protest lasted more than three hours as police tried to negotiate with protesters, ending in riot police using rubber bullets and pepper spray to disperse angry protestors outside the CFMEU headquarters.
Chanting protesters had accused the union of 'selling out' and caving in to the government's demands for mandatory vaccinations.
The industry is not due to reopen until next Tuesday, after the government shut it down for a fortnight in the wake of large numbers of positive Covid-19 cases spread at construction sites.
Victoria has reported a further 950 locally acquired Covid-19 cases on Wednesday with experts warning that the state's Delta peak could be twice as large as NSW's.
The Department of Health announced a further seven Covid-related deaths, taking the outbreak's death toll to 36.
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