According to the Associated Press, the city of Chicago has officially filed a federal lawsuit against the Department of Justice, alleging that the government's plan to withhold certain funds from sanctuary cities is illegal.

A "sanctuary city" is a city that limits its cooperation with the national government's efforts to enforce immigration law.

The city of Chicago is considered as a sanctuary city, and has been for several years.

The suit, which was filed this week by Mayor Rahm Emanuel, contains 46 pages and states, "neither federal law nor the United States Constitution permits the Attorney General to force Chicago to abandon … critical local policy [on immigrants]."

What triggered the suit are new federal public safety grant regulations that require cities to disclose information on illegal immigrants in police custody to ICE agents, and to cooperate with ICE activities more than Chicago law currently allows for.

Although Chicago is bringing the suit, the results of this case will affect cities across the Union, including Dallas, Los Angeles and New York.

Smaller cities have been put under federal scrutiny as well.

Recently, Attorney General Jeff Sessions sent letters to Baltimore, Albuquerque, and California's San Bernardino and Stockton that said if the cities' officials  do not comply with the new immigration guidelines, that the cities would suffer steep consequences.

The grant that Chicago would lose under the Trump administration rules isn't large in the grand scheme of things, clocking in at $2 million. However, because that money goes to help fund the city's police department, Chicago says both needs the money, and wants to make sure the administration can't put larger grants in jeopardy. 

"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."

As with all lawsuits, this case will take some time to come to court. To speed things up, the city says it plans to request a preliminary injunction this week. Should a judge grant it, the Trump administration would not be able to enforce the rule while the case is ongoing.