U.S. lawmakers acted Friday to close the country's borders to pollution-belching Mexican cars, a step that could affect thousands of daily commuters.

"Clearly a significant problem exists," said Brian Bilbray, the Republican Congressman from San Diego who introduced the bill that would allow U.S. Customs to stop and issue fines up to $400 on drivers of vehicles that don't meet emission-control standards.The bill - passed by a voice vote in a subcommittee of the House Commerce Committee - is designed to crack down on the thousands of commuters from Mexico who cross daily into the United States and account for 13 percent of the pollution in the San Diego area alone.