(4:46 p.m. EDT) -- Late on the evening of April 9, the U.S. Centers for Disease Control and Prevention issued new directives to the cruise industry, extending a "no sail" order for all ships with more than 250 passengers and crew onboard from operating within the waters of the United States.

The "No-Sail Order and Other Measures Related to Operations" extends the previous directive that was issued March 14, 2020, and could ban most cruises departing from or visiting the United States for 100 days from the date of issue, which is approximately July 23, 2020. The order could also be lifted or amended by the CDC director "based on specific public health or other considerations" or if the COVID-19 pandemic is no longer declared a public health emergency.

However, not all cruise lines are affected by the CDC's ruling.

Small-Ship Cruise Lines

Small ships with fewer than 250 passengers and crew are not affected by the CDC's ruling. In its April 9 order, the CDC report states that all cruise ships "with the capacity to carry 250 or more individuals (passengers and crew) with an itinerary anticipating an overnight stay onboard or a 24-hour stay onboard for either passengers or crew" are prohibited.

This allows small-ship lines like Alaska Dream Cruises, American Cruise Lines, Blount, Lindblad Expeditions and UnCruise Adventures to resume operations of their entire fleets before the expiration of the ruling.

Other lines, even ones based in the United States, aren't as lucky.  American Queen Steamboat Company's eponymous American Queen would be unable to operate, as it carries 436 passengers and 174 crew. That goes for the rest of the American Queen Steamboat company fleet, which all carry more than the mandated maximum of 250 people.  

Also affected by the ruling are Pearl Seas Cruises and Victory Cruise Lines, American-based lines that both have fleets carrying over 250 total passengers and crew.

The same goes for Norwegian Cruise Line's American-flagged Pride of America, which operates year-round out of Hawaii and would be unable to operate under these new regulations.

The CDC ruling lists no specific requirement for these vessels to be American-flagged. Most cruise lines flag their vessels in other countries including the Bahamas, Panama, the Netherlands, Italy and Norway,  meaning that lines with foreign-flagged smaller vessels could potentially call on American ports, or sail within American waters, prior to the expiration of the CDC's newest notice.  

This would include lines like Island Windjammers, SeaDream Yacht Cub, Variety Voyages, and Windstar Cruises (though only Wind Star and Wind Spirit are small enough to qualify).

European-based Cruise Lines

Cruise lines that operate primarily in Europe would not be affected by this ruling, as the CDC has no jurisdiction over operations outside American waters. This would apply to large cruise lines like MSC, which could potentially restart European sailings but which would be prohibited from operating its voyages to the Caribbean from Miami.

European river cruise lines and Europe-centric operators like Celestyal Cruises would also be able to restart as long as local authorities deem operations safe. Celestyal Cruises is headquartered in Cyprus.

Cruises Operating Out of Foreign Ports

Cruise Critic reached out to the CDC to see what impact these new regulations would have on lines that are based in the United States but flagged elsewhere who wanted to operate in Europe or out of other foreign regions like Canada and the Caribbean. Could Royal Caribbean, for example, send its ships to Europe or Canada to resume operations?

The answer, according to the CDC is yes, so long as those voyages don't begin or end in the United States, or enter U.S. territorial waters. That would eliminate voyages to certain parts of the Caribbean, Hawaii and Canada and New England for now, as well as transatlantic crossings between the United States and Europe. Lines like Royal Caribbean and others, however, could operate voyages in Europe or other areas of the world outside the CDC's jurisdiction.

Operators based outside of the United States -- companies like Celestyal Cruises, Fred.Olsen,  Hurtigruten, MSC Cruises, P&O, Sea Cloud Cruises, and Star Clippers --  would all be able to restart operations as soon as local authorities deem it safe to do so. These lines, however, would be prohibited from calling on American ports or entering American waters until the ban is lifted. This could result in significant itinerary changes or voyage cancellations, depending on the line.

This ruling also further affects cruises to Alaska. Canadian authorities had previously banned cruise ships from Canadian ports of call until July 1. The CDC's new regulations, while not affecting ships calling on Vancouver, would affect the ability for those ships to enter U.S. territorial waters in Alaska for as long as the ruling is in effect.

Could Cruise Lines Limit Capacity to Get Around This Regulation?

At this point, it doesn't look like it. The CDC ruling states that all ships with "the capacity" to carry 250 or more people are banned from operations.