AUSTIN — A new law aimed at cracking down on Mexican truckers who pull unlicensed trailers is instead making American companies and Rio Grande Valley officials nervous it could stifle cross-border trade.

The Legislature earlier this year passed House Bill 313 by Rep. Joe Pickett, D-El Paso, which requires so-called “phantom” trailers to be registered in either Texas or Mexico if they operate on the Texas border.

The North American Free Trade Agreement allows Mexican truck equipment registered in that country to move freely within a commerce zone inside the U.S. border, but some companies fail to maintain any valid registration, Pickett said.

‘We were going after the foreign carriers to begin with,” he said.

When the law took effect Sept. 1, Texas Department of Public Safety officers began issuing warnings to Mexican truckers pulling U.S. trailers with valid registrations from other states, telling those truckers their trailers had to be registered in Texas.

Pickett said he did not intend for the law to affect companies legally registered in other states and doing business here.

“I didn’t want to impede business in any form or fashion,” Pickett said. “I just want the bad actors to pay up.”

Trucking companies based in the United States have much at stake with how the new law is interpreted, said Les Findeisen, director of policy for the Texas Motor Transportation Association. They would have to register tens of thousands more trailers. They would also have a harder time bringing goods across the border.

“If enforced as DPS has interpreted, Mexican truckers may not be so eager to come to Texas and latch on to American trailers,” Findeisen said.

The measure could also wreak havoc on the trade-reliant border economy, said Rep. Armando “Mando” Martinez, D-Weslaco, whose district includes the San Juan headquarters for Spirit Truck Lines.

American companies with large factories in Reynosa and Matamoros count on Mexican truck companies to drive their goods and supplies to and from Mexico, Martinez said.

“You don’t want the maquiladoras to say, ‘We’re leaving.’” said Martinez, one of several Valley lawmakers working with Pickett to delay implementing the law.

Pickett said he has requested, through House Transportation Committee Chairman Mike Krusee, R-Round Rock, an opinion on the matter from Texas Attorney General Greg Abbott. He said he hopes DPS will delay issuing citations until the Legislature meets again in 2009 and clarifies the law further.

DPS officials are for now giving warnings to truckers who violate the new law, which is common practice for 90 days after any new law takes effect, said spokeswoman Tela Mange. After that, it is not clear whether DPS will ticket truckers, she said.

“All we can say is that we’re still sorting out what we’re going to do,” she said.