An immigration detainer is a notice that the Department of Homeland Security (DHS) issues to federal, state and local law enforcement agencies to advise that ICE intends to assume custody of an individual.  It serves three functions.

  1. To notify law enforcement that ICE will assume custody once the alien is no longer subject to detention;
  2. To request information from law enforcement about the alien; and
  3. To request that law enforcement hold the alien for up to 48 hours (excluding Saturdays, Sundays, and holidays) when the alien would otherwise be release so that ICE has time to assume custody.