Updated at 7:15 p.m. ET.
The U.S. Justice Department has escalated its approach to so-called sanctuary cities, writing at least eight jurisdictions Friday to put them on notice they could be failing to cooperate with immigration authorities.
Alan Hanson, the acting assistant attorney general for the Justice Department's grant-making arm, warned the cities that they're required to submit proof that they comply with federal immigration law.
"Failure to comply with this condition could result in the withholding of grant funds, suspension or termination of the grant, ineligibility for future ... grants, or other action, as appropriate," Hanson wrote.
The places receiving the letters include Chicago, New Orleans, Philadelphia, Las Vegas, Miami, Milwaukee, New York and Sacramento, Calif.
Attorney General Jeff Sessions has adopted a hard line on immigration, dating to his time in the U.S. Senate. Sessions links immigration to a variety of social problems, including what he calls a rise in crime.
In a statement accompanying the letters to sanctuary cities, the Justice Department said "many of these jurisdictions are also crumbling under the weight of illegal immigration and violent crime."
While murders and other violence are on the rise in some major cities, most scholars have concluded that crime remains near historic lows and that immigrants commit fewer crimes than U.S.-born citizens.
The Justice Department statement blasted New York for gang murders there, labeling them "the predictable consequence of the city's 'soft on crime' stance."
New York's murder tally is one of the lowest in the nation, according to data collected by the FBI. A spokesman for the New York Police Department, J. Peter Donald, responded on Twitter: "Did DOJ really say the NYPD is soft on crime?"
Later, Police Commissioner James O'Neill issued a statement pointing out that last year, New York experienced fewer shootings than since the city had started keeping records. To argue otherwise, as the U.S. Justice Department has done, "demonstrates a willful disregard of the facts," O'Neill said.
New York Mayor Bill de Blasio also weighed in, telling President Trump that if he believes New York is soft on crime, "then I invite him to come to NYC, look our officers in the eye and tell them."
In response, the Justice Department said the issue was the city's policies, not law enforcement officers:
"Unfortunately, the Mayor's policies are hamstringing the brave NYPD officers that protect the city, and only serve to endanger the lives of the hard working men and women of the NYPD who care more about keeping their city and country safe than they do about city hall politics."
In California, Attorney General Xavier Becerra said his state has a "right to determine how it will provide for the safety and general welfare of its residents and to safeguard their constitutional rights."
Becerra added: "Fearmongering and falsehoods will not intimidate our state into compromising our values. Federal threats to take away resources from law enforcement or our people in an attempt to bully states and localities into carrying out the new administration's unsound deportation plan are reckless and jeopardize public safety."
Earlier this week, Justice Department veterans warned that a tough approach to jurisdictions that refuse to follow federal immigration and marijuana laws could hurt community partnerships.
"I think it's cause for concern," said Miriam Krinsky, a former federal prosecutor who now works with newly elected district attorneys and state attorneys. "With federal money moving forward, there could be the potential for federal strings to be attached."
Sessions, who is touring the Southwest border this week, told MSNBC that most cities are cooperating. "We're pleading with the cities, let's don't have a fight over this," Sessions said earlier Friday. "So I hope we don't end into a fight, but we're perfectly willing to do whatever I can to ensure that we have the kind of unified effort that protects America."