Truckers carrying shipments into the United States from Canada and Mexico may be required to show passports at border crossings earlier than first planned.

The U.S. departments of State and Homeland Security disclosed in a Federal Register notice Friday that the deadline requiring passports could be moved up to Jan. 1, 2008, for all U.S., Canadian and Mexican citizens entering or re-entering the United States.

Congress in October extended the deadline for land and sea passport entry to June, 2009. But the final rule published Friday now states that these departments "are working to meet all requirements as soon as possible" to implement the Western Hemisphere Travel Initiative for land and sea travel. The target date now is "as early as Jan. 1, 2008."

Air travelers entering or re-entering the U.S. from Canada. Mexico and Bermuda -- estimated to be 21.9 million a year -- must present passports on arrival starting Jan. 23, 2007. The only exceptions are for U.S. citizens who are members of the armed forces traveling on active duty, merchant mariners on maritime business, and travelers who present a Nexus Air card.

The Nexus pilot program now running at Vancouver, British Columbia, uses iris-scanning to verify pre-screened U.S. and Canadian travelers.

Arrivals by sea were to have come under the air deadline but that was shifted to the land border deadline when it was decided that an alternative to passports for sea travel could be the Passport Card being developed by Homeland Security for land borders.

Canadians have historically been exempt from having to present passports on arrival in the U.S., instead using drivers' licenses or other photo identification. But State and Homeland Security estimate that well over 90 percent of Canadian citizens already carry passports.

For truckers driving to and from U.S. seaports, there had been some requests that the U.S. Transportation Workers Identification Card be accepted in lieu of a passport, since card holders are pre-screened. Those requests were rejected, since TWIC does not establish citizenship and can be issued to non-U.S. citizens.

For U.S. citizens, Washington estimates the cost of obtaining passports in the first year of the rule at $649 million, dropping to $92.9 million in the second year.