Mexico may stop some U.S. trucks from doing business south of the border in retaliation for the United States' refusal to allow Mexican trucks to make long-haul trips on U.S. highways.

Hector Marquez Solis, trade and NAFTA director at the Mexican Embassy in Washington, DC, said as much this week at a conference at South Texas Community College.

He says Mexico is running out of patience on the issue and officials are close to taking action, but he declined to comment on when or what type of action.

NAFTA allows truck companies in the United States, Mexico and Canada equal access to each other's infrastructure. But under pressure from the Teamsters union, the United States has barred access to Mexican carriers, citing safety and security concerns and lower wage standards.

Mexican and U.S. trucks are now allowed into a 20-mile buffer zone along each side of the international border.