WASHINGTON ― The Trump administration will attempt to block an agreement between the city of Chicago and the state of Illinois to reform the long-troubled Chicago Police Department, Attorney General Jeff Sessions said Tuesday.

The Justice Department has backed away from police reform in various contexts, but this will be the first time it’s actively attempted to intervene to prevent reform from moving forward. The unusual federal intervention on a negotiated agreement between state and city officials will likely draw a strong rebuke from both parties.

The Justice Department’s 2017 Chicago police investigation ― the largest ever federal probe of a city’s police force ― found that “broad, fundamental reform” was needed in Chicago. The report, issued by the Justice Department’s Civil Rights Division and released near the end of Barack Obama’s presidency, said that only independent monitoring could bring about reform.

After the Trump administration made clear it wasn’t interested in negotiating any agreements to reform police departments, Illinois’ attorney general got involved. Chicago Mayor Rahm Emanuel and Illinois Attorney General Lisa Madigan announced an agreement last month.

In a statement Tuesday, Sessions again made the dubious claim that a prior agreement between Chicago and the American Civil Liberties Union was responsible for a spike in homicides in the city.

“Chicago’s agreement with the ACLU in late 2015 dramatically undercut proactive policing in the city and kicked off perhaps the greatest surge in murder ever suffered by a major American city, with homicides increasing more than 57 percent the very next year,” Sessions said. “Now the city’s leaders are seeking to enter into another agreement. It is imperative that the city not repeat the mistakes of the past ― the safety of Chicago depends on it.”

“Accordingly, at the end of this week, the Justice Department will file a statement of interest opposing the proposed consent decree,” he said. “It is critical that Chicago get this right.”

Sessions said shortly after he became attorney general that he hadn’t read the Justice Department’s investigation into policing in Chicago.

Last week, a jury convicted Chicago officer Jason Van Dyke for the 2014 murder of 17-year-old Laquan McDonald. Days later, President Donald Trump urged the city of Chicago to embrace “stop-and-frisk” policing, inaccurately calling it an effective approach.

Ryan Reilly is HuffPost’s senior justice reporter covering the Justice Department, federal law enforcement, criminal justice and legal affairs. Have a tip? Reach him at ryan.reilly@huffpost.com or on Signal at 202-527-9261.