Italy’s decision to constrain cruise ship growth in Venice will likely change the way some cruise passengers enter and leave the city as it is phased in over the next few years.

Prime Minister Enrico Letta approved plans to limit or shut down cruise ship traffic in parts of the Venice lagoon.

His order is at least a partial victory for the No Grandi Navi (No Big Ships) movement that sprang up in Venice as megaships began to visit the city.

And it is a setback, at least for now, for cruise lines.

“This would certainly be a disappointing outcome from our perspective,” Carnival Corp. said in a statement, which went on to assert that “the cruise industry is an important economic driver for Venice and other communities around the world.”

The ruling does not ban cruise ships from docking in Venice, but it places restrictions on how many ships can transit the Guidecca Canal, which takes passengers past the city’s iconic St. Mark’s Plaza.

Starting in January, it requires a 20% reduction in the passage of ships larger than 40,000 gross tons. It limits the number of large ships that can dock at the city’s main cruise terminal, Venezia Terminal Passeggeri, to five per day, according to European press reports.

By November 2014, ships over 96,000 gross tons would no longer be permitted in the Guidecca canal.

In its statement, Carnival said that while no changes are currently being planned, “we will evaluate the ruling and see how it impacts our business in the long run.”

Royal Caribbean Cruises Ltd. also responded to the ruling, saying that it is reviewing its deployments for 2013 and 2014 to be sure they comply with the new regulations.

“We recognize visiting Venice during their cruise is a highlight of our guests’ vacation,” Royal stated. “We expect to continue with our scheduled port calls to Venice for our 2013 and 2014 itineraries.”

Last year, 661 cruise ships bearing 1.7 million passengers called at Venezia Terminal Passeggeri. No breakdown of ship size was immediately available.

For the industry, Venice has become a vital turnaround port, uniquely serving both western and eastern Mediterranean itineraries.

For the city, that means extra revenue. Cruise ship passengers and crews spend $255 million a year in Venice, according to a 2013 Cruise Market Watch study, ranking it eighth among world cruise ports and third in Europe, behind Barcelona and Rome (Civitavecchia).

Practically, the decision will first affect deployment decisions for 2015. Neither Carnival nor Royal has announced its 2015 itineraries. The squeeze would be most acute in the summer months when ships tend to migrate to the Med.

One solution is to develop a new channel to Venezia Terminal Passeggeri for large ships that bypasses the most historic part of Venice. Letta’s office said the order restricting ship size also authorized development of such a channel.

However, that would end the romantic entrance to the city past St. Mark’s Plaza, which is treasured by many cruise passengers.