Chicago's Mayor Rahm Emanuel is pushing back against the federal government.
On Monday, the city is filing suit against the Department of Justice, which announced it would withhold millions of dollars in police grant money from so-called sanctuary cities.
Emanuel is suing because he says new rules for a federal crime-fighting grant go against the Constitution and the city's values.
"Chicago will not let our police officers become political pawns in a debate," Emanuel said.
Last week, U.S. Attorney General Jeff Sessions said grant applicants have to share information about undocumented immigrants to federal officials if they want the funding.
But Emanuel said he refuses to choose between immigrant rights and having well-funded community police.
"We're going to act immediately," Emanuel said, "to make sure that there's a ruling by the court, as there's been on other issues as relates to immigration and refugee policies — where the court has basically stopped the Trump administration in its tracks."
Chicago was expecting to get $3.2 million from the grant to help with crime fighting this year.
"The Department of Justice cannot commandeer local law enforcement to carry out federal immigration law functions," said Ed Siskel, the city's lawyer. "We cannot be forced to violate our residents' constitutional rights."
Chicago Police Superintendent Eddie Johnson also expressed concern about the application guidelines.
"Our job is to investigate crime, our job is not to investigate immigration status or documentation," Johnson said.
Attorney General Sessions sent letters to four other cities last week warning them that they also wouldn't be eligible for funding: Baltimore, Albuquerque, N.M, and San Bernardino and Stockton in California.
A spokesman for the Department of Justice declined to comment.