Emanuel said U.S. Attorney General Jeff Sessions’ plan to withhold some federal grants from local police in so-called sanctuary cities violated the Constitution, stymied police anti-crime efforts and threatened the city’s long history as a place where immigrants have prospered.

“Chicago will not let our police officers become political pawns in a debate,” Emanuel said. “Chicago will not let our residents have their fundamental rights isolated and violated. And Chicago will never relinquish our status as a welcoming city.”

Those are themes the mayor has sounded repeatedly since Trump — whose campaign for office was built in part on a pledge to crack down on illegal immigration — last year became the presumptive Republican nominee. Emanuel’s message is viewed as politically advantageous in an overwhelmingly Democratic city with a minimal number of Trump supporters and a significant Latino population.

Emanuel’s latest effort to cite his pro-immigration bona fides came during a rare Sunday news conference at City Hall, alongside Corporation Counsel Edward Siskel, police Superintendent Eddie Johnson and a multiracial group of officeholders. It was just two days after Emanuel received widespread attention for telling a veteran news reporter he planned to sue the Justice Department.

And he’s likely to get further chances to sound off in the coming week. The city plans to file the paperwork “first thing on Monday morning,” officials said. But officials declined to release the lawsuit wording Sunday despite holding a news conference, leaving some details of the filing still unknown.

There’s also a possibility of other sanctuary cities taking the city’s side. “The city of Chicago may be the first to bring a lawsuit, but I’m also confident we will not be the last,” Emanuel said. Cook County Board President Toni Preckwinkle, who oversees what is considered a “sanctuary county” that also could lose funding, said in a statement that she supports the mayor’s effort. “We will assess our own legal options going forward,” she said.

Although Sessions’ threat to withhold money from the Edward Byrne Justice Assistance grant program from sanctuary cities is not new, the Justice Department late Thursday released conditions for new grant applications, said Siskel, the city’s top lawyer.

The conditions include complying with a federal law that bars restrictions on local police sharing immigration status information, providing unlimited police station access to federal officials searching for people in the country illegally and giving federal officials 48 hours’ notice of an arrested person’s release in cases of potential immigration violations.

“So-called ‘sanctuary’ policies make all of us less safe because they intentionally undermine our laws and protect illegal aliens who have committed crimes,” Sessions was quoted as saying in a July statement telegraphing the conditions. Department officials on Friday declined to comment on the mayor’s pledge to sue.

Chicago’s welcoming city ordinance bars police from providing federal Immigration and Customs Enforcement officials access to people in local custody unless they are wanted on a criminal warrant or have serious criminal convictions. It also prohibits allowing ICE agents to sue police facilities for interviews or investigations and bars on-duty officers from responding to ICE questions or talking to ICE officials prior to a person’s release from custody.

Nevertheless, the city maintains it is in compliance with federal immigration laws. And Siskel said holding people “longer than necessary” because ICE wants 48 hours’ notice would be a “violation of their Fourth Amendment” rights related to searches and seizures. And Siskel maintains that the Justice Department does not have the authority to add requirements to a grant program created by Congress or “commandeer local law enforcement to carry out federal immigration functions.”

Siskel also said the city chose to file a lawsuit now, rather than after it had been denied a grant, because of the new conditions set last week. He said the city will ask a judge to declare the new Byrne grant conditions unlawful and unconstitutional before they affect the city.

The city is planning on receiving $3.2 million this year in Byrne grants — primarily used to buy police vehicles, radios, SWAT equipment and Tasers — an amount equal to three-hundredths of 1 percent of the entire $9.8 billion city budget. But Emanuel said the equipment it buys is “needed” and called the effort to pull those grants “the camel’s nose under the tent. ... The Trump Justice Department is trying to set a precedent, but then it allows it to widen it to other grants.”

The mayor also made the case that if police cooperated with ICE agents, it would make people in this country illegally who can help prevent or solve crime fearful of cooperating with police. “We need to strengthen the bonds between all residents, regardless of status, with our police officers, not break those bonds,” he said.