Chicago will keep fighting President Donald Trump's immigration policies with a federal lawsuit alleging it's illegal for the federal government to withhold public safety grants from so-called sanctuary cities, Mayor Rahm Emanuel announced Sunday.

The mayor said Chicago won't "be blackmailed into changing our values, and we are and will remain a welcoming City."

The lawsuit will be filed Monday.

Officials said there are new qualifications for a public safety grant requiring cities to share information with federal immigration authorities. City officials allege those qualifications are unconstitutional.

Chicago received about $2.3 million in such grants last year, which have been used for buying police vehicles.

Chicago is being helped by two outside law firms on a pro bono basis.

Federal officials have threatened to withhold federal funding for sanctuary cities, saying they don't comply with federal laws.

Asked to comment on Emanuel's statement, U.S. Department of Justice spokesman Ian D. Prior said via email: "In 2016, more Chicagoans were murdered than in New York City and Los Angeles combined. So it's especially tragic that the mayor is less concerned with that staggering figure than he is spending time and taxpayer money protecting criminal aliens and putting Chicago's law enforcement at greater risk."