The Justice Department is calling it a "last chance" for local governments to demonstrate they are in compliance.
The cities cited by the Justice Department were New York, Chicago and surrounding Cook County, Ill., New Orleans and Philadelphia.
The section Sessions references, Section 1373, is a federal statute barring local and state governments from limiting communication regarding residents' immigration or citizenship status with federal officials.
Proponents of "sanctuary cities", like Kenney, say they create trust between police and immigrants, who otherwise might be afraid to report crimes.
U.S. Attorney General Jeff Sessions said in a statement that these cities "adopt the view that the protection of criminal aliens is more important than the protection of law-abiding citizens and of the rule of law".
The U.S. Department of Justice, in separate letters to Chicago Police Department Superintendent Eddie Johnson and Cook County Board President Toni Preckwinkle penned Wednesday, highlights several active policies created to shield undocumented immigrants from being unduly targeted by law enforcement entities.
The feds are giving what they call a "last chance" warning to NY that the city's immigrant-friendly policies may cost it federal grants.
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Broadly speaking, a sanctuary city is one that doesn't necessarily enforce federal immigration laws or hand over undocumented immigrants to federal agencies. ". We urge jurisdictions to not only comply with Section 1373 but to establish sensible and effective partnerships to properly process criminal aliens".
The city of New Orleans has two weeks comply with federal immigration law or risk losing federal money.
NY refuses requests by the feds, known as detainers, to hold undocumented immigrants arrested for most crimes and turn them over for possible deportation. "On its face, the Department has determined that this. appears to restrict Chicago police officers" ability to "assist' federal immigration officers by sharing information regarding immigration status with the federal officers". In a letter dated Wednesday, Hanson noted that the city's 2016 Edward Byrne Justice Assistance Grant - commonly known as JAG funding - required Philly to comply with the statute.
The determinations came after the Justice Department earlier in the year had asked several local jurisdictions to detail their compliance with the law in order to make a determination about their eligibility for certain federal grants.
"As you know, the city welcomed immigrants long before I was ever mayor", Kenney said at the time.
The Justice Department has also flagged Cook County, Illinois, where Chicago is located.