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.

The new rules were to have kicked in January 2008, but they were postponed in part by fears that they would hinder trade and tourism.

Homeland Security Secretary Janet Napolitano told reporters this week that she knows some Americans are unaware of the new requirements or haven't gotten around to getting a passport. The process can take a month or more.

"We'll work with them at the border," she said. That may involve being pulled aside while border agents confirm identity and citizenship.

Cruising already is a sea of confusion.

For instance, cruisers who begin and end their trips in the same U.S. port are not required to show passports under the new law. Technically, they can use a driver's license and birth certificate.

The Cruise Lines International Association says individual carriers reserve the right to require certain identification, including passports and that would-be cruisers check with individual cruise lines when booking.

It's too early to say whether the new rules will further slow travel and harm tourist-dependent areas such as Mexican border towns.

A record 30% of Americans hold passports, the State Department says. But applications, which had been rising, are down in this recessionary year (7.1 million issued through April, vs. 10.3 million in the same period last year).

The cost for an adult passport ($100 purchased in person; $75 by mail) and $45 passport card for first-time adult purchasers ($20 by mail) may deter some vacationers. As might the wait to get them.

So who might profit from the new rules?

Puerto Rico and the U.S. Virgin Islands — St. Thomas, St. John and St. Croix — are United States territory and continue to be passport-free zones.