The military contingents, decked out in fatigues, ballistic vests, helmets and assault rifles, are an imposing presence.
The Mexican strategy is not to stop migrants at the largely unguarded 600-mile border with Guatemala, much of it in remote terrain. Mexico lacks the personnel and infrastructure for such a massive undertaking.
Rather, the aim is to intercept migrants along the major northbound roads, and to discourage others from attempting the trip.
As a result, fewer people appear to be making the journey.
In July, U.S. immigration authorities on the Southwest border apprehended or turned away 82,000 foreigners -- down from a 13-year high of 144,000 in May.
Public buses and vans making their way north from the Guatemalan border are methodically stopped and subjected to immigration inspections, as are all passing cars and trucks.
"It's a lot different now -- people here respect us a lot more now," said Jose Armando Ramos Hernandez, a 10-year veteran of the National Immigration Institute, Mexico's immigration enforcement agency. "Before, we used to receive threats. Now with the national guard, everyone stops, no one threatens us."
On a recent morning at the checkpoint, Ramos pulled two 17-year-olds off a northbound bus. Both men presented Mexican birth certificates. But Ramos was suspicious: They spoke Spanish with the lilting country accents of Guatemala's northwest highlands.
Under questioning, Ramos said, the two eventually admitted they were Guatemalans and had purchased the birth certificates for about $300 each in Comitan, where there is now a brisk trade in such documents.
The two men were loaded into a white Chevrolet van with barred windows and processed for deportation.