Leinenweber, in his 41-page ruling, said that the city could suffer "irreparable harm". Leinenweber wrote that Chicago has shown a "likelihood of success" in its arguments that Sessions overstepped his authority with the requirements.
Forcing reluctant cities to help round up illegal aliens was a key component of the president's campaign pledge to rid the US of "bad hombres" entering from Mexico.
Debates over immigration often involve more histrionics than policy. Leinenweber did side with the Trump administration on preserving an existing requirement for the grants - certifying compliance with a federal law that mandates local jurisdictions communicate immigration status information to the federal government - which was put in place originally by the Obama administration.
"It means essential resources for public safety will not come with unlawful strings attached", Mr. Emanuel said, "and the Trump Justice Department can not continue to coerce us into violating and abandoning our values". Chicago has already applied for $1.5 million in Byrne grants, which are used for personnel, training, supplies and other areas. More than 30 other jurisdictions filed court briefs in support of Chicago's lawsuit.
Federal records show the Justice Department doled out $1 billion in Byrne JAG money to state governments, $430 million to nonprofits and $136 million directly to cities and counties past year.
"This is not just a victory for the city of Chicago". Throughout his presidential campaign, he vowed to pull federal funding from such cities unless they began cooperating and collaborating with Immigration and Customs Enforcement (ICE) to facilitate deportations.
The U.S. Department of Justice will not be permitted to withhold grant funds from cities that refuse to assist federal immigration officials to pursue suspected undocumented immigrants, a judge ruled Friday.
Sessions described Chicago's lawsuit in August as "astounding".
San Francisco, Los Angeles and the state of California also sued the federal government over the threat of losing Byrne grants.
"As sheriff, part of my job is enforcing our constitution and the law, regardless of what cheap political points Albany politicians are looking to score", Howard, a Republican, said in a statement.
Trump is eyeing tougher immigration measures and has pledged to build a wall on the U.S.
The case involves cities that vowed to shield illegal immigrants. The ruling is likely temporary as the law is expected to change, with Congress giving that authority to the DoJ.
Immigration hard-liners, including in the White House, are concerned that a law allowing those young people to become US citizens, would then allow them to sponsor their parents and close relatives for lawful permanent residence, increasing the number of immigrants in the country. Trump later announced he was working on an agreement to protect them.
The administration said cracking down on illegal immigration would also be key to stopping violent gangs like MS-13. "We can get you to a sanctuary city where that city will help shield you from immigration".