U.S. Attorney General Loretta Lynch planned a news conference on Monday to announce a "law enforcement action" relating to Chicago, the Justice Department said.
The Monday announcement follows reports on Sunday that the department would open an investigation into the Chicago Police Department after protests over how it handled the case of a black teenager shot by a white police officer.
A person familiar with the matter confirmed on Sunday that there were would be a "patterns and practices" investigation but would not elaborate. Such investigations determine whether the department systematically violates constitutional rights.
The civil probe follows murder charges filed against the police officer in the October 2014 killing of 17-year-old Laquan McDonald, who was shot 16 times. The shooting was caught on videotape, which was not released until the charges were filed last month.
Officer Jason Van Dyke was charged with first-degree murder in the death. Shortly afterwards, the city released a patrol car video of the shooting, which showed Van Dyke had fired all the shots.
The Justice Department launched investigations into police departments in Ferguson, Missouri, and Baltimore after police actions raised concerns about discriminatory policies in those cities.