From the New York Times:
A proposal by the Obama administration that would grant Mexican truckers greater access to Texas roadways — and far beyond — would be a boon to businesses in the state, supporters say. But unions, the Teamsters in particular, say the plan would cost American jobs.
A provision in the original 1994 North American Free Trade Agreement would have allowed long-haul truckers from Mexico to move about the United States without mileage restrictions, but it was never put into effect. Today, tractor-trailers entering the United States from Mexico (and vice versa) are limited to traveling within a 20-mile to 25-mile radius of ports of entry. There, Mexican truckers must drop their goods, which are then picked up by American truckers to be transported to their final destinations.