The department sent letters Friday to cities its inspector general previously identified as having rules limiting the information that can be provided to federal immigration authorities, including Sacramento, Chicago, New York and Philadelphia.
"A federal, state or local government entity or official may not prohibit or in any way restrict any government entity or official from sending to, or receiving from, the Immigration and Naturalization Service information regarding the citizenship or immigration status, lawful or unlawful, of any individual", the letter said.
Still, if the jurisdictions fail to prove they are in full compliance, they could lose the Office of Justice Programs Byrne JAG grant, which provides funding for personnel, training, and equipment, among other things.
The letters, signed by acting Assistant Attorney General Alan Hanson, came after both President Donald Trump and Attorney General Jeff Sessions emphasized the importance of fighting sanctuary policies, which protect undocumented immigrants by not fully cooperating with federal authorities.
The referenced law says that local government can not restrict local enforcement departments from sharing a person's immigration status with federal immigration officers.
New Orleans was among the 100 communities that "limit cooperation" with the federal government, according to a list the Trump administration put out in March.
Zach Butterworth, Mayor Mitch Landrieu's executive counsel and director of federal relations, said the city drafted its policies in consultation with federal immigration and Homeland Security officials.
The grants under threat-which amounted to roughly $24.5 million for Chicago previous year, according to the Center for Tax and Budget Accountability, -go in most part to law enforcement efforts. To argue otherwise, as the U.S. Justice Department has done, "demonstrates a willful disregard of the facts", O'Neill said. "To say we're soft on crime is absolutely ludicrous".
"People are scared, and because of that, they're less willing to report crime", Butterworth added. Clark County Sheriff Joe Lombardo, the elected head of the Las Vegas Metropolitan Police Department, said the city and county were wrongly labeled sanctuary cities. That means it will hold people for an extra 48 hours, long enough to be arrested by immigration authorities.
Police operate the Clark County Detention Center in Las Vegas, where Lombardo said four jail guards are assigned to notify ICE when risky criminals are identified during booking. Sessions links immigration to a variety of social problems, including what he calls a rise in crime.
A number of sanctuary cities have sued over the executive order. "My far greater concern is the proactive dissemination of misinformation, fear, and intolerance".