WASHINGTON – Opponents of a pilot program giving Mexican trucks greater access to U.S. highways won another round Thursday in their battle with the Bush administration.

The Senate Appropriations Committee voted 20-9 to block the program, which opponents say erodes highway safety and threatens U.S. jobs. The language, however, was attached to a transportation spending bill that's unlikely to be enacted before the president leaves office in January.

It's not the first time lawmakers have tried to thwart the program. Last December, Congress cut off funding to implement the program, which permits up to 500 trucks from 100 Mexican motor carriers full access to U.S. roads.

But a Department of Transportation lawyer found a loophole that has allowed the program – established last September – to go ahead. Thursday's provision makes doubly clear lawmakers' intent to block the program.

Sen. Byron Dorgan, D-N.D., predicted the administration would lose a lawsuit pending in federal court challenging the Transportation Department's interpretation that last year's law – which blocked taxpayer funds from being used to “establish” the program – doesn't apply to the program since it was established before the law passed.

The amendment adopted Thursday says the government could not in “in any way permit” the program to go ahead.

“The Department of Transportation has already defied the intent of Congress once, and they are not going to get away with it again,” Dorgan said. “With this amendment, this program will finally come to an end.”

Opponents have been fighting the measure – part of the 1994 North American Free Trade Agreement – since it was first proposed, saying the program will erode highway safety and eliminate U.S. jobs. And they say that there are insufficient safeguards to make sure Mexican trucks are as safe as U.S. carriers.

Supporters of the plan say letting more Mexican trucks on U.S. highways will ultimately save American consumers hundreds of millions of dollars. And they say U.S. trucking companies will benefit since reciprocal changes in Mexico's rules permit U.S. trucks new access to that country.

Before, Mexican trucks have had to stop within a buffer border zone and transfer their loads to U.S. trucks.

Still, there's widespread opposition to the program within Congress. The House voted without a roll call in last July to block the program and the Senate followed with a 3-to-1 vote in September to block it despite administration assurances that safeguards are in place to “ensure a safe and secure program.”