The buses rumble into town day and night, dumping migrants in a city many didn’t even know existed.

But instead of landing closer to the U.S. border, they are being hauled roughly 1,000 miles in the opposite direction — deep into southern Mexico in a shadowy program meant to appease the Biden administration and ship migrants far from the United States.

Mexican authorities rarely publicly acknowledge the busing program, making it much less contentious than the efforts by Republican governors to transport migrants to blue states that have become political theater in the United States.

Yet the busing program is exposing the chasm between the Mexican government’s rhetoric promoting a humanitarian approach to migration, and the country’s role as a heavy-handed enforcer of U.S. border objectives, leaving many migrant families stranded to fend for themselves.

“I asked the agents, ‘How can you treat us like dirt?’” said Rosa Guamán, 29, from Ecuador. She was detained with her husband and two children by migration agents in April near the border city of Piedras Negras. Nobody told them they were being taken to Villahermosa, an oil hub in southeastern Mexico, until they were well on their way.