The Trump administration intensified its threats to crack down on so-called sanctuary cities that refuse to comply with federal immigration authorities, sending letters Friday to nine jurisdictions warning it would withhold coveted law enforcement grant money unless they document cooperation.

The letters went to officials in California and in major cities including New York, Chicago, Philadelphia and New Orleans, all places the justice department’s inspector general has identified as limiting the information local law enforcement can provide to federal immigration authorities about those in their custody.

Attorney general Jeff Sessions has increasingly warned that the administration will punish communities that refuse to cooperate with efforts to find and deport immigrants in the country illegally.

In a statement Friday, the justice department said the recipients of its letters are “crumbling under the weight of illegal immigration and violent crime”.

After a raid led to the arrests of 11 MS-13 gang members in California’s Bay Area “city officials seemed more concerned with reassuring illegal immigrants that the raid was unrelated to immigration than with warning other MS-13 members that they were next,” the department said.

The federal law in question says state and local governments may not prohibit police or sheriffs from sharing information about a person’s immigration status with federal authorities. Friday’s letters warn officials they must provide proof from an attorney that they are following the law or risk losing thousands of dollars in federal grant money that police agencies use to pay for anything from body cameras to bulletproof vests.

The money could be withheld in the future, or terminated, if they fail to show proof, wrote Alan R Hanson, acting head of the office of justice programs, which administers the grant program, which is the leading source of federal justice funding to state and local communities.

The targeted jurisdictions also include Clark County, Nevada; Cook County, Illinois; Miami-Dade County, Florida; and Milwaukee County, Wisconsin.

They were highlighted in a May 2016 report by the justice department’s inspector general that found they have policies or rules that interfere with information-sharing among local law enforcement and immigration agents.

The Orleans Parish sheriff’s office, for example, has a policy to decline all requests by Immigration and Customs Enforcement to keep a suspected deportable immigrant in its custody long enough for immigration authorities to arrest the person unless that person is charged with certain violent crimes, according to the report.

It also pointed to a Miami-Dade County rule that allows its corrections department to honor detainer requests only if ICE agrees in writing to reimburse the county for costs and only if the inmate has a prior felony conviction, among other constraints.

The Obama administration warned cities after the report’s release that they could miss out on grant money if they did not comply with the law, but it never actually withheld funds.

The grants in question are based on population and support an array of programs, technology and equipment for local law enforcement agencies, which can use the money at their discretion.

Sessions said earlier this week that sanctuary cities undermine efforts to fight violent gangs.