The UIL and CGIL trade unions marchedin Bologna on Thursday to demand action on health and safety after this week's explosion at Enel Green Power's Bargihydroelectric plant on Lake Suviana near the Emilian capital, as the death toll rise to five, with two others missing, feared death.
The disaster, in which five other people were injured, is the latest in a long series of deadly workplace accidents in Italy.
Police said at least 1,500 people took part in the demonstration, marching behind a banner that read "Enough Now".
The unions' members are also striking for eight hours in EmiliaRomagna on Thursday, doubling the length of an already-planned nationwide general strike that is especially affecting public transport.
Firefighters said on Wednesday that there was little hope of finding the missing people alive.
At the time four people were still unaccounted for, but several firebrigade identified the location of two bodies on Thursday.
The divers had not yet been able to extract those corpses, sources said.
Investigators have opened a probe into alleged culpable homicide and culpable disaster.
Bologna Chief Prosecutor Giuseppe Amato said the probe would look into "procurement and subcontracting", an issue the unionssay is a major factor.
"These are sub-contract deaths," said Bologna CGIL Secretary Michele Bulgarelli.
"It is a day of anger because, after the shock, I think that yesterday's statement and press conference by Enel Green Powerwas absurd, unacceptable and unworthy of a civilized country.
"The offloading of responsibility in the procurement chain seesit list three or four (contractor ) companies.
"But up to today we have no official information about which companies employed the employees (involved)". Enel Green Power CEO Salvatore Bernabei stated that "we do notdeserve this kind of statement" and that "there is no subcontracting chain".
On Wednesday he had said that top companies had been chosen for the work being done at the plant.
"In order to carry out this technological upgrade of supply, assembly and testing (operations), we had chosen the best companies in the field of electricity and hydroelectricity: Siemens, Abb, Voith," Bernabei said.
"When I turn to a contractor, that contractor is synonymous with prestige and seriousness.
"You have to ask the contractors (about the work subcontractedout), who, in turn, can turn to other specialists, because the work we are doing here is work that can only be done by specialists".