The Italian cabinet is set to discuss emergency measures to keep large cruise ships out of Venice lagoon, three government sources say.
The government decided to act after the United Nations culture organisation UNESCO threatened to put Italy on a blacklist for not banning liners from the World Heritage site, one of the sources said.
The legislation will take immediate effect, the sources said, without giving further details.
It is likely to affect the business of cruise companies such as Carnival Cruises.
Francesco Galietti, Italian director of the international cruise industry trade association CLIA, said the group welcomed an alternative route for cruise ships so the latest government move was "a major step forward".
Rome has passed legislation in the past to limit liners' access to one of the world's most famous tourist sites, but an alternative docking point is not yet ready.
Residents protested in June when the 92,000 tonne MSC Orchestra sailed through the lagoon en route for Croatia and Greece, attracting the attention of international media.
In April, Prime Minister Mario Draghi's government approved a decree to build a terminal outside the lagoon where passenger vessels over 40,000 tons and container ships can berth without passing in front of Saint Mark's Square, the city's most famous landmark.
The call for bids to build the terminal was published on June 29.
In the meantime, large boats were told to dock at the industrial port of Marghera, but even this intermediate solution is not yet ready because Marghera lacks a suitable docking point for liners.
Galietti said he understood the government would also appoint a special commissioner to fast-track the docking station at Marghera, which was "a welcome development."
Venice residents and the international community have been urging governments for years to ban large ships passing through the lagoon, creating pollution and threatening the stability of its buildings and ecosystem.
Such concerns clash with the interests of port authorities and tourist operators who say the city needs the business offered by the cruise industry.
Alessandro Santi, who heads Federagenti, a national shipping lobby, said the government was taking no account of the industry and its approach was "regrettable and creates resentment".
He accused it of listening to UNESCO and international culture lobbyists while ignoring local "citizens and business people".
"Limiting the passage of ships won't solve the difficulties of Venice as a city," he said.