Texas Congressman Joaquin Castro is demanding to know why the Trump administration is shuttling migrant kids to a bare, unregulated tent city in the stifling West Texas desert. In a letter to Health and Human Services Secretary Alex Azar dated Oct. 2 and obtained by VICE News, Castro asked whether any children have died or been injured in the tent city, how the government intends to protect the children, how long they’re supposed to stay there and whether any employees of the tent city are receiving background checks, among other questions. In an interview with VICE News, the Democrat congressman also called on Homeland Security Secretary Kirstjen Nielsen to resign over the “family separation” practice stoked by the Trump administration’s “zero tolerance” stance on illegal border crossings. “It’s sad, it’s frustrating, it’s enraging,” Castro added. “There needs to be a restoration of humanity in this process.” The New York Times reported earlier this week that hundreds of migrant children ages 13 to 17 were transported via bus to a tent city in Tornillo, Texas — moved in the middle of the night, without notice, supposedly to prevent escape attempts. Previously, the children were housed in licensed, monitored shelters across the country that provided education and access to legal counsel, but those shelters are now close to or at capacity, according to the Times.

1,600 children have been transferred to the West Texas tent city so far, with more being sent there each week, the Times reported. The move is meant to be temporary, but it’s not clear how long they’ll be kept there. Castro told VICE News that he visited the Tornillo facility shortly after it opened in June, when it was holding a couple hundred children and officials with Health and Human Services were saying it would close in July. Because of a loophole in federal policy, the tent city is considered emergency housing and doesn’t have to abide by the same government regulations imposed on migrant children shelters, which can control for staffing ratios, health care and education, he said. “Since then, not only has it remained open with no definite date for closure, but it’s also expanded two or three or four times,” Castro said. He recalled that the tents were air-conditioned but there was “kind of a stale air” and “the kids just looked listless, they looked like they didn’t know where they were, what was going to happen to them.” He intends to visit again sometime this month.

The tent city was initially opened in June to temporarily host a few hundred children, but has since expanded to house 3,800 undocumented kids and will remain open through the end of the year, the Times reported. Many of the children crossed the border alone, without their parents.

The shelter is run by BCFS Health and Human Services, a San Antonio-based nonprofit that runs the facility under short-term contracts, and otherwise provides emergency relief services, according to local media reports. In the Tornillo tent city, meanwhile, the kids are given workbooks without any formal schooling and have limited access to legal services, the Times reported. The living spaces are cramped and teeming with kids.

“They seem to be shuffling some of these kids like hot potatoes,” Castro said.