Most U.S. citizens cruising in the Western Hemisphere are exempt from new passport regulations that took effect on June 1.

The final phase of the Western Hemisphere Travel Initiative requires U.S. citizens to have a passport when returning via land or sea from Canada, Mexico, Bermuda and Caribbean nations.

Or, Americans must have one of several other documents, including a driver's license with RFID chip or a passport card. The passport card costs less than a passport and is only valid for travel by land or sea.

But cruisers are not as affected because of a loophole exempting passengers on "closed-loop sailings," or itineraries that begin and end from the same U.S. port.

Passengers on closed-loop cruises must now travel with two forms of ID: a valid, government-issued photo ID and proof of citizenship. So on a roundtrip cruise from Miami, passengers now need a driver’s license and a birth certificate, for example.

Most U.S. cruises are closed-loop, but a notable exception is a Panama Canal cruise from Florida to California, which now requires passengers to have a passport.

For more information on passport rules, visit www.getyouhome.gov.