Due to be filed later on Monday, the lawsuit accuses Trump and Attorney General Jeff Sessions of acting unconstitutionally in forcing cities like Chicago to cooperate with federal immigration authorities.

“We are not going to be in a position between picking our values of who we are as a welcoming city and ... strengthening our police department,” Emanuel said on radio show on Sunday. "We find it unlawful and unconstitutional to be as a city coerced on a policy, and we think we have a strong case."

Although Chicago stands to lose a relatively small $3.2 million public-safety grant that it uses for police equipment, Emanuel said he would still sue the administration.

In general, "sanctuary cities" offer safe harbor to undocumented immigrants and often advance the enforcement of federal immigration laws without municipal funds or resources.

In April, the Department of Justice said it would defund those cities that refuse to allow federal immigration authorities access local jails and information about undocumented immigrants among other things.

Under the new instructions, police departments are required to inform federal officials of an illegal immigrant’s release at least 48 hours in advance. Legal experts have warned that the requirement might lead to longer detentions, violating the person’s rights.

The department specifically named Chicago and New York City as communities that are "crumbling under the weight of illegal immigration and violent crime."