PHOENIX, Ariz. --- The U.S. Department of Transportation is expected to begin issuing operating permits to Mexican firms today to allow their freight trucks to roll into the United States. Last week, an appeals court in San Francisco denied an emergency petition to halt the Bush administration's one-year pilot plan. The appeal was filed by the Teamsters union, the Sierra Club and consumer group Public Citizen. The groups argued for the emergency stay based on safety issues. The pilot program represents a major policy shift since Mexican trucks have not been allowed past the 25-mile commercial border zone since 1982. Mazzella DeLaney, a spokesperson for the Federal Motor Carrier Safety Administration, told the Arizona Daily Star that all trucks in the program must pass a rigorous mechanical inspection. Moreover, drivers must be screened for drug and alcohol use, she said.