Jones Act

Federal Law prohibits travel between two contiguous U.S. ports. For example, you cannot board the ship in New Orleans and then debark in Tampa. Such travel would constitute point to point transportation between two U.S. ports, which is prohibited on foreign flagged ships. Any guest who insists on debarking under these circumstances accepts responsibility for any and all resulting penalties.

Ha!  I'm glad to see a law aimed directly at punishing Alaska has some blowback on the rest of the US.  I found this on the Carnival Cruise lines website.

I swear, the more you learn about the US federal government, the more contempt worthy it becomes.