Mexican President Vincente Fox has threatened to close his country's border to U.S. trucks if Mexican trucks aren't granted full access to U.S. highways. Many Mexican truckers say they don't want to haul beyond the border's 20-mile zone.

"If there continues to be resistance and there is no agreement, it will simply mean Mexican trucks will not go over there because they are not permitted or wanted," Fox told news reporters. "But neither will there be American trucks here."

The U.S. Senate approved a bill last week calling for tough safety standards for Mexican trucks operating in the United States, a move that was hailed by independent truckers (OOIDA), organized labor and highway safety groups. The approval followed a House vote to bar Mexican trucking companies from seeking operating licenses in the United States. President George W. Bush has threatened to veto the bills saying they violate U.S. obligations under NAFTA.

Mexico's Congress passed a measure last week calling for the Fox administration to close the border to U.S. trucks if Washington fails to comply with the NAFTA rules