Tougher ID requirements begin June 1 for citizens returning to the U.S.

— -- On June 1, U.S. citizens returning from Canada, Mexico, Bermuda and parts of the Caribbean by land or sea will face stiffer documentation requirements.

Passports, passport cards, Enhanced Driver's Licenses or "trusted traveler" cards will have to be shown, unless voyagers are youngsters or on certain exempt cruises.

(U.S. citizens already need a passport to return via air from Mexico, Canada, Bermuda and Caribbean islands except Puerto Rico and the U.S. Virgin Islands.)

The stepped-up requirements are the final phase of a Department of Homeland Security/State Department anti-terrorism policy called the Western Hemisphere Travel Initiative, which took effect in January 2007 with passports required to fly back from neighboring countries.

"The mission is to strengthen border security while facilitating legitimate travel," says Joanne Ferreira, a spokeswoman for U.S Customs and Border Protection.

The various entry cards and information on how to get them are detailed on the agency's website getyouhome.gov.

Passport cards, which look like driver's licenses, have been offered since July and can be used to drive or walk across the border from Canada or Mexico or to take ferries or cruises. They're not accepted for international air travel.

Enhanced Driver's Licenses, embedded with technology that refers border agents to a stored record in a government database, are currently being issued by only four states: New York, Vermont, Michigan and Washington State.

Other forms of acceptable land-and-sea border crossing documentation: "trusted traveler" cards such as SENTRI, NEXUS and FAST (for truckers), which require more screening to obtain. Those with passport cards, enhanced licenses and other cards embedded with identity information can use scanners to speed their trip through some checkpoints.

Those under 16 or teens 16 to 18 who are traveling with an organized group to Canada, Mexico, Bermuda and the Caribbean will need only a birth certificate, the Customs and Border Protection agency says.