Slipping over the border to Baja for the weekend, roadtripping to Quebec, or sailing to Bermuda for some pink sand-and-rum swizzle therapy won't be as easy as it used to be: Starting June 1, 2009, U.S. citizens seeking re-entry to the United States by land or sea from Canada, Mexico, Bermuda, and the Caribbean (excluding Puerto Rico and the U.S. Virgin Islands) will be required to show valid passports, or “Western Hemisphere Travel Initiative”-approved documents.

This final phase of the WHTI (rules affecting air travelers went into effect in January 2007) requires returning citizens to show traditional passports ($100 new, $75 renewals), or a number of other newly approved “smart” documents embedded with radio frequency identification, or RFID, technology: a U.S. passport card ($45), NEXUS (U.S.-Canada travel, $50) or SENTRI (U.S.-Mexico travel, $122) Trusted Traveler Program cards, or a state-issued “enhanced” driver’s license (available in Michigan, New York, Vermont and Washington, $80 average).

There are, however, a few exceptions to the new rule: Cruise ship passengers embarking and returning to the same U.S. port after sailing to Canada, Mexico, or the Caribbean need only a birth certificate or government-issued photo ID, such as a regular driver’s license. Also, children under 16 returning from neighboring countries will be readmitted with just a birth certificate.

The government hopes the initiative will aid in homeland security—and speed border wait times by 6–8 seconds per person. Still, some Americans are wondering how they can afford the required documentation, and business-owners on both sides of the borders are worried that more stringent controls will mean fewer travelers—and less money. Plus, there’s growing concern from personal freedom advocates over the slow sanctioned creep of the use of RFID technology to track citizens.

Considering only 30 percent of Americans actually have the required documents, we predict passport offices will (again) be inundated with requests—one of the original reasons for the staged rollout. So, if you’re driving to your cousin’s in British Columbia this summer and don’t yet have a passport, start your application today—and get in line.

Adrien Glover is Travel + Leisure's online deputy editor.