WASHINGTON — A senator wants Congress’ investigative arm to determine whether the Transportation Department has broken the law by spending federal money on a program allowing Mexican trucks on U.S. roads.

Sen. Byron Dorgan, D-N.D., called for the investigation by the Government Accountability Office a few hours after Transportation Secretary Mary Peters warned of economic losses if Mexican trucks are prohibited from driving deep into the U.S.

Peters has been fighting in court to prevent the program’s end. But Dorgan and others say Congress prohibited spending money on the program last year.

“When Congress passes a law that says no funds can be used for this program, we mean no funds can be used for this program,” Dorgan said in a news release. “The Department of Transportation cannot simply pick and choose which laws they want to follow and which laws they want to break.”

Dorgan said the agency is violating the Antideficiency Act, which prohibits spending federal money that has not been authorized or appropriated.

The North American Free Trade Agreement gave Mexican trucks greater access to U.S. roads beginning in 1995. But the U.S. only opened the roads to a few trucks when the pilot program began last September.

Long-standing opposition from labor and safety groups had kept the trucks off most U.S. roads. Without the program, Mexican trucks are confined to about 25 miles beyond the border, where goods they bring are picked up by U.S. truck drivers.

Peters said Monday the agency is not violating the law. The law prohibits using funds to establish the program, she said, but the money is being used on the existing program. The agency has made similar arguments in the 9th U.S. Circuit Court of Appeals, which is considering an appeal by the International Brotherhood of Teamsters to stop the program.

The action was a prelude to a potentially bitter Senate committee hearing on the program planned for Tuesday, with Peters scheduled to testify.

Earlier Monday, Peters said U.S. business would suffer if the trucking program is stopped.

“Should Congress ... end the cross-border trucking, Mexico has every right to impose fees and tariffs on the very goods we see before us this morning and many more,” Peters told a news conference. Before her were tables loaded with apples, ham, soybeans, rice, eggs, canned chili and meat, beef, milk, whiskey and other products.

Todd Spencer, vice president of the Owner-Operator Independent Drivers Association, called Peters’ claims “economic fear-mongering.”

“The program is supposed to work both ways across the border, and yet there are very few signing up on either side,” Spencer said in a statement. “Big businesses want the cheap labor, but for a number of reasons trucking companies on both sides of the border don’t want to get involved.”

The latest numbers from the Transportation Department show 18 Mexican carriers with 62 trucks and six U.S. carriers with 46 trucks are participating in the program. Up to 500 trucks from 100 Mexican carriers can participate.

Mexican trucks have made 322 crossings into the U.S., while U.S. trucking companies have made 683 crossings into Mexico.

James Hoffa, International Brotherhood of Teamsters president, said he doesn’t buy Peters’ argument that Mexico will sanction U.S. goods with higher tariffs in retaliation. Mexico has a $70 billion trade surplus because of NAFTA and “they’d be foolish to do it,” Hoffa said.

Ricardo Alday, spokesman for the Mexican Embassy in Washington, said Mexico is keeping its options open.

On the Net:

Transportation Department: http://www.dot.gov