The Teamsters union, the Sierra Club and other public-advocacy groups asked a U.S. court to block a pilot program that would allow Mexican trucks from as many as 100 companies to drive into the United States starting this weekend.

The organizations sought an emergency stay until they get more assurances that the vehicles comply with U.S. environmental, security and safety regulations, said Sierra Club spokesman Josh Dorner. The trucks would be allowed to drive into the United States under a U.S. Transportation Department one-year trial plan.

Loads from Mexico now must be transferred to U.S. trucks and drivers when the freight enters the United States. The new plan would save time and money for Mexican trucking companies by letting some of them move shipments around the United States themselves. The program might start as soon as this weekend, Dorner said.

''What a slap in the face to American workers opening the highway to dangerous trucks on Labor Day weekend,'' Team Please see Trucks, C11

sters President Jim Hoffa said in a statement.

The union also is seeking proof that U.S. trucks would have the same rights to travel in Mexico that the Mexican trucks would have in the United States. The DOT said Aug. 17 that reciprocal access for U.S. truckers was a requirement for the trial to begin.

The DOT inspector general's office, the agency's internal watchdog, said Aug. 21 that the United States needs tighter controls on Mexican truck and bus drivers with driving violations and greater ability to inspect buses on the border before the rules take effect. The U.S. House of Representatives voted in July to block the program. The Senate hasn't voted.

Lawyers for the Teamsters and other groups approached the U.S. agency last Monday in an unsuccessful attempt to persuade them to delay the program, the groups said. The agency plans to begin the trial after submitting a response to concerns on Friday, according to the filing.

''We are working closely with the Department's Inspector General as his office completes an additional assessment of the program, and we prepare a detailed response to that report,'' the U.S. department said in an e-mailed statement. ''Congress has required that both of these steps be completed before the agency moves forward with'' the trial program.

An agency spokesman declined further comment as to when the rule may take effect.

The attempt to block the rule was filed today in the U.S. Court of Appeals for the Ninth Circuit in San Francisco, said Jonathan Weissglass, lead attorney for the groups in the dispute. The consumer advocacy group Public Citizen and the Environmental Law Foundation also joined in the petition.

Letting Mexican trucks operate in the United States would benefit companies such as Con-way Inc., the largest U.S. regional trucking company. Con-way in July bought closely held Contract Freighters Inc., which said 40 percent of its business begins or ends in Mexico. Celadon Group Inc., an Indianapolis-based trucking company, has a division in Mexico and might gain business under an open-border policy.

The 1994 North American Free Trade Agreement required the United States, Mexico and Canada to open their roads to trucks from all three countries. Canadian trucks have full access to U.S. roads, while Mexican trucks are limited.