Is illegal to disembark cruise ship?

It is not illegal to disembark a cruise ship - people do it all the time! However, for vessels operating in the United States, an Act of Congress called the Jones Act prevents passengers from disembarking in any port except the one they embarked in. Therefore, it prevents passengers from using cruise ships as a "taxi". A violation of this can result in heavy fines from Customs & Border Protection to both the vessel and the passengers. The Jones Act also requires foreign ships operating in the United States to touch a foreign port for at least a few hours during their itinerary.