BELLINGHAM, Wash. - New rules that take effect Monday mean anyone trying to cross the U.S. border from Canada or Mexico will need a passport.

Merchants fear the requirement will cost them business - and everyone else is bracing for the possibility of longer lines at the U.S.-Canadian border.

The rules are being implemented nearly eight years after the Sept. 11 attacks and long after the 9/11 Commission recommended the changes. They were delayed by complaints from state officials who worried the restrictions would hinder commerce.

J.J. Melrose, who has a shop in Bellingham, is one of those who shares that concern.

"We do see a lot more Canadians come down here and shop," he said. "It does make a difference - it adds more sales."

Peter Lee, who also operates a shop in Bellingham, is worried, too.

"They (Canadians) are big shoppers - they are always coming two or three people together," he said.

The new rules also could mean longer lines at the border crossings.

A spokesperson for U.S. Customs and Border Protection says 80 percent of people who cross the Canadian border already using a passport or equivalent document.

But, that still leaves thousands of people who don't. If they're in line, and they're not ready with passport in hand - they could clog the border, which could create nightmarish backups for everyone else.

Border agents will be cutting people some slack at first, until everyone gets used to the new rules. But anyone who tries to cross from Canada or Mexico into the U.S. will get a warning and be required to undergo a background check.

Documents that will meet the new requirements include a valid passport, an enhanced driver's license, a U.S. passport card or a Nexus card.

For more information about the new border crossing requirements, visit the following web sites:

Department of Homeland Security border crossing information - www.dhs.gov/xtrvlsec/crossingborders/

List of compliant documents - www.getyouhome.gov/html/eng_map.html

U.S. Customs and Border Protection web site - www.cbp.gov