PHILADELPHIA (CBS) — One of President-elect Donald Trump’s campaign promises to remove federal funding from so-called sanctuary cities has Philadelphia Mayor Jim Kenney gearing up for a fight.

With Philadelphia being a sanctuary city, officials do not cooperate with federal laws requiring undocumented immigrants to be held in custody for non-violent crimes and potentially deported.

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Trump has said he will withhold federal funding from cities which don’t comply, which could hinder money going to low-income housing and highway maintenance.

Kenney said he is ready for the fight.

“All the federal government has to do is go over to a federal magistrate, get a warrant and we’ll be happy to turn that person over to them, but to expect us to hold people for 48, 72 hours without charge, to me, is unconstitutional,” the mayor told CBS 3’s Greg Argos.

Experts predict the fight will be a costly one.

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“The purse strings are very important here,” attorney Linda Dale Hoffa said.

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This could be fought in both state and federal court.

“I don’t know if it’s going to be a losing battle, but I do know that a lot of lawyers are going to be involved,” Dale Hoffa said. “There is going to be a lot of litigation.”

Kenney said the city would have to determine whether to take the Trump White House to court over funding if it was withheld.

“We will have to determine what it is they’re trying to take away and how much it is and how it’ll affect us and we’ll make that determination into whether or now we’ll seek legal protection,” Kenney said. “We’re going to resist it every way we can.”

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However, for right now, no one knows what could be cut, but it appears a big battle is ahead.