Attorney General Jeff Sessions has made good on his threat to cut Justice Department grants to so-called “sanctuary cities” that refuse to cooperate with federal immigration enforcement. On Friday his subordinates sent letters to nine such jurisdictions demanding proof of compliance.

The letters, sent to the relevant authorities in New York City, Chicago, New Orleans, Philadelphia, Las Vegas, Miami, Milwaukee, and the “sanctuary state” of California, makes clear that Byrne Grants, a major program by which the federal Department of Justice funds local law enforcement, will be withheld if these jurisdictions do not do their part to enforce federal immigration law.

In order to avoid losing their funding, the cities and California must provide the Justice Department documented proof of compliance with 8 USC § 1373 no later than June 30. That law states that:

[L]ocal 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 accompanying press release noted the skyrocketing crime rates that have plagued these non-compliant jurisdictions and stressed the need to cooperate on immigration in order to fight growing transnational crime organizations like MS-13.

Combating the recalcitrance of santuary cities has been a cornerstone of Sessions’s policy so far at the Department of Justice. Friday’s move makes good on an earlier pledge to withhold federal funding from sanctuary cities.