"Many of these jurisdictions are also crumbling under the weight of illegal immigration and violent crime", the Justice Department said as it sent the letters.
Mayor's spokesman Seth Stein calls that "alternative facts". As an example, the department pointed to the murder rate in Chicago, citing the rising rate at which murder incidents are occurring in the city.
He says the Trump administration's grandstanding is out of touch with reality.
Emanuel, a White House chief of staff in the Obama administration, has beefed up the city's efforts to protect immigrants living in the country illegally, including establishing a legal fund with taxpayer money to help those facing deportation. Then there's Trump, who campaigned on a promise to defund sanctuary cities, only to find his immediate power to do so limited.
A spokeswoman for the California Board of State and Community Corrections said some of the federal funding in question went to local communities after emergencies, including San Bernardino after a mass shooting there in 2015.
The Justice Department could withhold federal funding for law enforcement if it deems New York City isn't cracking down on illegal immigration. Defiance is likely to continue until the courts order sanctuary cities to comply.
"President Trump and Attorney General Sessions have to make a decision immediately about this statement, because it has denigrated not only the people of New York City, but the men and women of the NYPD", de Blasio said during a news conference. The letter warned that federal grant money could be withheld if the city can't document cooperation.
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 Department of Justice says the mayor's policies "are hamstringing" the police". He noted that the law referenced in the Justice Department's letter was on the books before President Donald Trump took office.
On Friday, the Department of Justice sent a letter to authorities in Chicago, New York, New Orleans, California, Philadelphia, Las Vegas, Milwaukee and Miami, saying they need to prove by the end of June that they are adhering to federal laws on immigration, or they face the risk of losing federal grants.
The Trump administration is putting on notice officials in several major cities that are sanctuaries for immigrants in the USA illegally.
Justice Department records show New Orleans received almost $266,000 in grant money through the program in fiscal 2016.
In a message on immigration compliance, Attorney General Jeff Sessions said New York City isn't doing enough to stop crime.
They were singled out in a May 2016 report by the Justice Department's inspector general that found local policies or rules could interfere with providing information to immigration agents.