Sanctuary cities are finding themselves suddenly on the defensive, as the Justice Department and state legislatures are looking to force cooperation between local police and federal immigration enforcement.

In the last few weeks, state and federal policymakers have taken steps to rein in cities that bar their police officers and jails from working with Immigration and Customs Enforcement to identify and deport illegal immigrants who have committed crimes. In response, Chicago Mayor Rahm Emanuel on Monday sued in federal court to block those moves by the administration.