Eddie Johnson and Cook County Board President Toni Preckwinkle, along with a handful of other so-called sanctuary cities around the country, come as Mayor Rahm Emanuel continues a federal court fight with Attorney General Jeff Sessions.
The jurisdictions have until October 27 to provide "additional evidence" that their laws and policies do not run afoul of the statute or face the possibility of losing federal law enforcement grants.
Broadly speaking, a sanctuary city is one that doesn't necessarily enforce federal immigration laws or hand over undocumented immigrants to federal agencies.
"Under my Administration, the New Orleans Police Department has and will continue to follow all federal laws; however, the NOPD will not be the federal government's deportation force".
Additionally, the Justice Department said subsequent investigations found Miami-Dade County, Fla., and Clark County, Nev., where Las Vegas is located, were already in accordance with federal immigration law, though previously they had been listed otherwise.
The city has said its policies are legal, and vowed to sue if money is actually taken away.
City and county officials did not immediately say how they would respond to the letters. Perhaps ironically, another major Trump supporter, Republican former New York Mayor Rudy Giuliani, memorably offered a dramatic defense of policies that shielded immigrants from persecution while running City Hall in the 1990s.
Sessions, in a statement accompanying the warnings, said "jurisdictions that adopt so-called "sanctuary policies" also 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".
If the government finds the cities and county are violating the statute that calls for information sharing with federal immigration officials, it says it could decide to cut federal funds for law enforcement. Requiring New Orleans Police to demand information about immigration status, local officials argued, would only lead to immigrants fearing and mistrusting police, rather than cooperating with them.
"We urge jurisdictions to not only comply with Section 1373 but to establish sensible and effective partnerships to properly process criminal aliens", he added. Though this rule is aimed at barring questions about immigrants' legal status, DOJ says it could be interpreted to bar NYPD members from requesting immigration info from federal immigration officers, which would be illegal.