Sanctuary laws and policies seek to build trust with immigrant communities by restricting cooperation with deportation and other federal enforcement efforts, but Sessions said the documents he seeks may prove San Francisco and other agencies are violating US statutes.
Sessions has made it one of his best needs to get serious about sanctuary cities, a term that portrays more than 300 nearby governments that have restricted their collaboration with elected movement authorities.
White House spokeswoman Sarah Sanders said mayors can not "pick and choose what laws they want to follow".
At issue are grants named for Edward Byrne, a slain NYPD officer - who de Blasio pointed out was gunned down while protecting a Guyanese immigrant who was set to testify in a criminal case.
As a result of the threats, Democratic New York City Mayor Bill de Blasio abruptly canceled Wednesday's meeting with President Donald Trump in which he would join over 100 mayors from across the country to discuss plans about infrastructure.
"R$3 ecipient jurisdictions that fail to respond, fail to respond completely, or fail to respond in a timely manner will be subject to a Department of Justice subpoena", according to a U.S. Department of Justice press release.
Attorney General Jeff Sessions holds a news conference at the Department of Justice on December 15, 2017.
Frank Shuftan, spokesman for Cook County Board President Toni Preckwinkle, said the county's sanctuary ordinance already complies with federal law.
"We can not allow people to pick and choose what laws they want to follow".
A number of mayors said they would boycott a meeting between mayors and White House officials because of the DOJ threats.
They threatened to subpoena city, county and state instructions to police on how to treat undocumented people and cooperate - or not cooperate - with federal officials in rounding them up.
Speaking at a news conference at the opening of the U.S. Conference of Mayors' 86th annual Winter Meeting in Washington, D.C., Los Angeles Mayor Eric Garcetti called the letter "pure politics" and said every mayor "cares more about the public safety of our people than anybody living outside of our cities".
The state of California and the city of Los Angeles were among several USA jurisdictions Wednesday who were warned they may face subpoenas if they don't willingly relinquish documents showing they aren't withholding information about the citizenship or immigration status of people in custody.
Annie Lai, a professor and immigration expert at UC Irvine School of Law, said the Justice Department was "taking the few openings they still have legally and stretching them as far as they can to exert pressure on jurisdictions to abandon their immigrant protective policies". These values were affirmed some 30 years ago in state statute, which are in full compliance with federal law. The letter sent out today by the Department of Justice demands that Denver provide documentation to verify that we, in fact, uphold the Constitution by declining to do ICE's job for them.
"Together, we will use every legally viable tool at our disposal to protect the American people from risky criminal aliens and from the people that place their protection over the protection of law-abiding citizens", the official said.