The answer could play a key role in a legal battle over the facility’s fate. And it has bigger implications, too.

In a letter sent late Tuesday to the heads of the Department of Homeland Security, Immigration and Customs Enforcement, and FEMA, the lawmakers expressed concern that the Trump administration's decision to use what lawmakers called a "novel state-run immigration detention model" could violate federal law and make the federal government less accountable for the conditions at immigrant detention centers.