The Department of Homeland Security is escalating its clash with so-called sanctuary states, warning multiple states they could face legal action, CBS News has learned.

The Department of Homeland Security has escalated its clash with so-called sanctuary states this week, warning California, New York, and Illinois in letters obtained by CBS News that refusal to honor immigration detainers could trigger federal legal action.

In letters dated Sept. 10, Acting U.S. Immigration and Customs Enforcement Director Todd Lyons ordered the attorneys general of the three states to declare within two days whether they would comply with “thousands of ICE detainers” lodged against individuals in state custody, according to DHS. Immigration detainers are formal requests by ICE asking local jails and prisons to notify the agency before releasing an individual, and to hold them briefly so federal agents can take undocumented migrants into federal custody.