HARLINGEN — Interstate truck and bus drivers across America may find themselves pulled off the highway if state troopers or vehicle inspectors find they can’t speak English.

The requirement has been on the books for decades, but enforcement has begun before Mexican trucks are allowed in the U.S. interior as of Sept. 6.

“We have found people in violation of this for a number of years and we’re working feverishly to correct it,” said John Hill, head of the Federal Motor Carrier Safety Administration.

Since 1971, federal law has said that commercial drivers must read and speak English “sufficiently to understand highway traffic signs and signals and directions given in English and to respond to official inquiries.”

Hill said the language deficiency was found mostly in the commercial zone that varies from 25 miles to 75 miles north of the Mexican border, but since inspectors there are bilingual and Mexican truckers are not allowed past that zone, it hasn’t been an issue.

But after more than a decade of legal wrangling, U.S. highways are opening up.

The North American Free Trade Agreement in 1994 called for Mexican and U.S. trucks to travel freely throughout one another’s nations, but the provision was stalled by labor unions and environmental groups’ arguments that the trucks are unsafe.

A pilot program allowing a limited number of already approved Mexican trucks to pass the border zone was set to begin as early as Saturday, but Hill said no trucks will pass beyond the border zone pending a final report by the inspector general. The program is now set to take effect Sept. 6.

The language requirement is part of a long checklist - including criminal background and drug and alcohol tests - that carriers must pass to go into the interior, ranging from criminal background and drug and alcohol testing for drivers to complete

U.S. commercial drivers going into the Mexican interior, part of the reciprocal agreement, will have to speak Spanish.

Under the new enforcement regulations, drivers who can’t speak English in the commercial zone may be ticketed and fined. Those beyond the border zone will also be pulled off the road.

Richard Henderson, director of government affairs for the Commercial Vehicle Safety Alliance, a nonprofit group representing federal and state highway inspectors and highway patrols, said the requirement was a “no brainer.”

“The bottom line is safety,” Henderson said. “Obviously, if (the driver) can’t speak English he’s not going to know what some of the regulations are.”