May 20, 2009 (United Press International) -- New passport rules taking effect June 1 won't affect Americans cruising round-trip from a U.S. port and staying in the Western Hemisphere, travel experts say.

The majority of international passengers will still allowed to use a birth certificate and government-issued photo I.D. to return to the United States on a cruise ship, the South Florida Sun-Sentinel reported Wednesday.

Beginning June 1, the United States is requiring all adult citizens traveling internationally by sea to show passports when returning from Mexico, Canada, Bermuda or Caribbean nations.

Travel industry and government officials told the Sun-Sentinel there is an exemption for U.S. citizens cruising round-trip from a U.S. port and traveling only within the Western Hemisphere.

However, passengers on itineraries that start at one port and finish at another, known as open-jaw cruises, will be subject to the passport rule.

Carnival Cruise Lines spokeswoman Jennifer De La Cruz says open-jaw itineraries are rare.