We have this short document called the Constitution and, thank you, it discourages keeping people in jail for no reason other than the government’s whim or vague suspicion. The Fourth Amendment, for instance, says “No warrants shall issue, but upon probable cause, supported by oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.” So to search your stuff, or seize you and take you into custody, the government has to have a reason, good enough to convince a judge there is probable cause, which a reasonable suspicion based on fact that an accusation is true. The Fifth Amendment, part of the first 10 we call the Bill of Rights, includes something called the Due Process Clause, saying nobody can be denied life, liberty and property without it. Roughly speaking, they can’t throw you in jail, or keep you in jail for anything but a very brief period, without some kind of court proceeding.
So where is the constitutionally required warrant and probable cause when an agent from federal Immigration and Customs Enforcement (ICE) scans the jail log and decides to ask that certain people not be released from custody, so that their immigration status can be further scrutinized? What cause could there be? An address? Possession of suspicious documents? A database hit? A name ending with Z perhaps?