Saturday's protest was expected to be bigger than a peaceful march on Friday in which thousands of people took to the streets as partial transport strikes across the country cancelled dozens of flights and snarled buses and trains.
Italy is struggling to shake off a two-year recession that has pushed unemployment to record highs and parliament is discussing a draft budget for next year that includes more cuts.
"We're giving money to the bankers! We're like a car going down a cliff," Paolo Ferrero, leader of the Communist Refoundation party, said at a demonstration by the USB union federation.
Firefighters, steel workers, civil servants and students were among a few thousand people who took part in the protest march through central Rome.
The Italian capital's Fiumicino airport said 143 flights had to be cancelled because of a strike by baggage handlers and civil air transport staff.
Protesters in the capital were set to camp out in a square overnight ahead of Saturday's rally that officials are concerned could lead to violent confrontations.
Over 3,000 police officers are expected to patrol the demonstration as it snakes through the capital.
Many shops were expected to remain closed with their shutters down for the duration of the rally in a bid to minimise damage to property.
On Friday, police picked up five French nationals and expelled them from the country, accusing them of being "professional anarchists" planning to disrupt the protest, Italian media reported.
Officers also pulled over a suspect van which was found to be carrying hammers, clubs, billiard balls and fire extinguishers.
The rally will be led by an anti high-speed rail movement and an association for rights to housing.
Reports suggest demonstrators may be planning to occupy buildings, including hotels, in protest over a lack of accommodation for poor families who have been hit hard by the recession, the longest Italy has suffered since the post-war period.