There are almost 400 sanctuary cities, counties or states across the nation that provide safe haven to illegal immigrants.

Sanctuary policies vary, but generally limit local cooperation with federal authorities by instructing public employees not to hold or report illegal immigrants to U.S. Immigration and Customs Enforcement unless there is a warrant for the person’s arrest. A complete list, compiled by the Ohio Jobs and Justice Political Action Committee, can be found here.

Proponents of the law say immigrants — even those here illegally — contribute to the overall health of local economies. They say it is unfair to tear apart families and deport people who have not committed crimes. They also argue that it allows illegal immigrants to feel safe enough to go to the police.

"I firmly believe it makes us safer," San Francisco Sheriff Ross Mirkarimi told CNN's "The Lead with Jake Tapper" in 2015. "We're a world-renowned city with a large immigrant population. ... From a law enforcement perspective, we want to build trust with that population."

Opponents say sanctuary policies protect criminals and foster unsafe environments.

“Sanctuary policies, official or de facto, result in safe havens (or safer havens) for illegal aliens involved in a variety of criminal enterprises. Sanctuary policies inhibit the ability of law enforcement officers to accurately identify foreign nationals which makes it more difficult to uncover their illegal activities,” Ohio Jobs and Justice PAC founder Steve Salvi said on his website.

The Pew Research Center estimates there to be more than 11 million illegal immigrants living throughout the U.S.

President-elect Donald Trump has made a promise to cut federal funding to sanctuary cities and states as a way to force them into compliance with federal deportation laws.

On the campaign trail in August during a speech on his intended immigration policy he said he would "block funding for sanctuary cities. We block the funding. No more funds. We will end the sanctuary cities that have resulted in so many needless deaths.”

He went on to warn of the consequences for cities that do not heed federal laws.

“Cities that refuse to cooperate with federal authorities will not receive taxpayer dollars, and we will work with Congress to pass legislation to protect those jurisdictions that do assist federal authorities," Trump said.

Since he was elected Nov. 8, Trump has not said whether he will hold true on his promise.