The suit revolves around specific conditions Sessions announced in July
for a federal program, the Edward Byrne Memorial Justice Assistance Grant, or Bryne JAG, which provides federal funding to support local law enforcement efforts.
"(The executive branch) may not unilaterally concoct and import into the Byrne JAG program sweeping new policy conditions that were never approved (and indeed were considered and rejected) by Congress and that would federalize local jails and police stations, mandate warrantless detentions in order to investigate for federal civil infractions, sow fear in local immigrant communities, and ultimately make the people of Chicago less safe," attorneys for the city wrote in Monday's filing.
In July, Sessions announced that going forward DOJ will only provide JAG grants to those that certify compliance with a federal statute that requires localities to share immigration information about individuals with the federal government, allow federal immigration access to local detention facilities, and provide the Department of Homeland Security at least 48 hours advance notice before local officials release an undocumented immigrant wanted by federal authorities.
Chicago claims that it already complies with the main federal law at issue, the new conditions are unconstitutional, and would require Chicago to violate state law.
"Chicago can comply with the Department's new notice condition and provide DHS with 48 hours of lead time prior to arrestees' release only if the City detains arrestees for longer than they would otherwise be held in the City's custody, which implicates constitutional, state-law, fiscal, logistical, and other legal concerns," the city argued in the court filing.
Chicago Mayor Rahm Emanuel defended his city's lawsuit Monday, telling CNN the DOJ's new stipulations against so-called sanctuary cities "undermines our actual safety agenda."
"We want you to come to Chicago if you believe in the American dream," Emanuel, a Democrat, told CNN's Poppy Harlow on "Newsroom." "By forcing us, or the police department, to choose between the values of the city and the philosophy of the police department, in community policing, I think it's a false choice and it undermines our actual safety agenda."
He continued: "So we're going to be filing a case saying that the Justice Department is wrong on constitutional legal grounds that is we will always be a welcoming city ... but it also is true that our police department is part of a neighborhood, part of a community, built on the premise of trust."
Emanuel's office said in a statement over the weekend that the Trump administration's "latest unlawful misguided action undermines public safety and violates" the Constitution. He said the city is challenging the administration "to ensure that their misguided policies do not threaten the safety of our residents."
The Justice Department will have an opportunity to respond to Chicago's lawsuit, but in the meantime pushed back against Emanuel's assertions on Monday.
"This administration is committed to the rule of law and to enforcing the laws established by Congress," Sessions said in a statement released Monday evening. "To a degree perhaps unsurpassed by any other jurisdiction, the political leadership of Chicago has chosen deliberately and intentionally to adopt a policy that obstructs this country's lawful immigration system."
Sessions' statement added, "This administration will not simply give away grant dollars to city governments that proudly violate the rule of law and protect criminal aliens at the expense of public safety. So it's this simple: Comply with the law or forego [sic] taxpayer dollars."
Last year Chicago received $2.3 million in JAG funds. Over the years, the city has purchased SWAT equipment, police vehicles, radios and Tasers with the money.
Applications for the grants in fiscal year 2017 are due September 5, which the city claims places it in an "untenable position" by essentially making it "accept the Department's new unconstitutional grant conditions, which would wipe away policies that have built trust and cooperation between law enforcement and immigrant communities over the decades; or stand on its rights and forfeit crucial funds that it and the eleven other jurisdictions on whose behalf it submits Byrne JAG applications have counted on for more than a decade to provide critical (and, at times, lifesaving) equipment to Chicago Police officers and critical services to Chicago residents," attorneys said in Monday's filing.
Jamie Gorelick -- a partner at Wilmer Hale who also represents Ivanka Trump and Jared Kushner on non-Russia related legal issues
, is one of the many attorneys who is listed as pro bono counsel on the suit.
Emanuel, who also worked as former President Barack Obama's chief of staff, also was asked by CNN about John Kelly's new role as White House chief of staff to President Donald Trump.
"Look, he has one of the toughest jobs in the world ... he's brought order, there's no doubt. He's a person with great order. He's brought discipline, no doubt, to that effort," Emanuel said.