If ICE places a “notice detainer” on an individual who is incarcerated and they are not being held on anything else, ICE has 48 hours (not including weekends or holidays) to pick up your client. A hold any longer subjects the facility to civil penalties. The form the jail will have is an I-247.
Many jails do not abide by this rule. Attached is a sample letter I submit on behalf of clients who are subject to this overstay. In every instance I have used it, I have found an immediate response from the local facility, and ICE immediately arrives and processes the individual. See link below for sample letter.