Starting Tuesday, air travelers who are citizens of Canada, Mexico and Bermuda, as well as U.S. citizens returning home, must with few exceptions display passports to enter the United States.

The new rule brings them under the same rules that apply to all other travelers worldwide.

Canadian Minister of Public Safety Stockwell Day has made clear that Canada considers this first phase affecting only air travelers to be reasonable. However, Canada is worried that rules about land and sea, which will take effect sometime between January 2008 and June 2009, could clog land borders and disrupt trade.

"We need to ensure that we do not build walls between us," Canadian officials recently wrote. Day and Homeland Security Secretary Michael Chertoff plan to meet on Thursday.

Sens. Patrick Leahy, D-Vt., and Ted Stevens, R-Alaska, whose states border Canada, pushed through legislation last year to postpone implementation of the land and sea phase of the law until alternatives can be developed.

Rep. Louise Slaughter, D-N.Y., has also expressed concern that the land and sea portion was being rushed, saying it appears the Bush administration is "moving full-steam ahead with a misguided policy."

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Until now, citizens traveling in the Western Hemisphere usually needed to display little more than a birth certificate or driver's license to cross U.S. borders.

The new rules were mandated by Congress in 2004 following the terrorist attacks of Sept. 11, 2001, and were recommended by the 9/11 Commission.

The only acceptable alternatives to the official passport will be a document carried by U.S. merchant mariners; the NEXUS Air card issued to some U.S. and Canadian frequent travelers; and active duty members of the U.S. Armed Forces.

The bigger hurdle is scheduled to begin as soon as January 2008, when passports will be required for travelers by land and sea—a much larger category of people.

Homeland Security Department spokesman Jarrod Agen said "we're looking at alternatives." He said department officials have been meeting with Canadians and border community officials to determine how best to provide some flexibility to the law's requirements.

Agen added that a so-called PASS Card has been discussed as a cheaper and more convenient alternative to the passport. The card would be about the size of a credit card and likely cost considerably less than a passport, but it wouldn't replace the passport for travel to most of the world.
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