Brushing up on English has taken on new urgency for future and current truck drivers after President Donald Trump issued an executive order saying truckers who don’t read and speak the language proficiently would be considered unfit for service.

“A driver who can’t understand English will not drive a commercial vehicle in this country. Period,” Transportation Secretary Sean Duffy said in May while announcing enforcement guidelines that took effect in June.

Updated U.S. Department of Transportation procedures call for enhanced inspections to determine if commercial motor vehicle operators can reply to questions and directions in English, as well as understand highway traffic signs and electronic message boards.

Truckers who learned English as a second language are concerned they may lose their jobs if they make a mistake or speak with a heavy accent while under questioning. Some have worked to improve their English fluency by taking classes, reciting scripts and watching instructional videos.

“If it’s not the language that you prefer to use daily, you may get a little nervous and you may feel, ‘What if I say the wrong thing?’” said Jerry Maldonado, chairman of the board of the Laredo Motor Carriers Association, a trade association in Laredo, Texas, that represents approximately 200 trucking companies. “It’s going to be, at the end of the day, the interpretation of the officer, so that makes people nervous.”

Requiring truck drivers to speak and read English isn’t new, but the penalty for not meeting the proficiency standard is becoming more severe.

To get a commercial driver’s license, applicants must pass a written test and be able to name the parts of a bus or truck in English as they check tire inflation, tread depth, lug nuts and coolants.

The revised policy reverses guidance issued nine years ago, near the end of then-President Barack Obama’s final term, according to the Federal Motor Carrier Safety Administration. In 2016, the agency said drivers whose English skills were found lacking could receive a citation but not be prohibited from working. Before that, the penalty was getting placed on “out-of-service status.”

This article was provided by The Associated Press.