Two men died and a third was in critical condition in hospital after an accident at a building site near Settimo Milanese on Friday.
The three Egyptian workers fell from a height of 20 metres when scaffolding collapsed beneath them.
The men are thought to be illegal immigrants who were paid for their work off the books.
In April the former centre-right government pushed through a decree on safety reforms which included measures to protect immigrant workers, who are often hired by lower-tier subcontractors seeking to contain costs and skimp on safety regulations.
The reforms also set hefty fines for employers failing to follow regulations and tried to tighten control of the subcontracting chain.
But according to ANMIL, an association representing injured workers, the country needs far more work safety inspectors for the reforms to make any difference.
The association said that if every Italian business were to be checked by the number of staff currently available, each would receive a visit once every 23 years.
Friday's accident comes two days after six workers died from inhaling toxic fumes at a sewage plant in Sicily and adds to a string of workplace deaths that have put pressure on the government to crack down on the application of the safety laws.
On Thursday Welfare Minister Maurizio Sacconi promised a ''special plan'' to tackle workplace accidents and said the key to improving inspection rates was ''close collaboration'' between unions, industry bosses and government bodies.
Reacting to Friday's accident, Sacconi said the workers' deaths were ''another reason to speed up'' the plan, which he hopes to bring into effect by the start of the summer.
