The Department of Justice has filed a lawsuit against the city of Denver after its public officials attempted to ban masks for federal law enforcement officers.

Dig deeper: The department is suing the city and county of Denver, Mayor Michael Johnson, attorney Michiko Ando Brown, and Police Chief Ronald Thomas.

In addition to the mask ban, the city has also required federal officers to present identification, a requirement the DOJ claimed "threatens the safety of federal officers." Big picture view: The lawsuit against Denver is one of a series of lawsuits brought on by the Civil Division which targets policies it says are "designed to thwart federal law enforcement across the country." The backstory: California became the first state to ban most law enforcement officers from wearing facial coverings under a bill that was signed in September following a summer of high-profile raids by immigration officers in Los Angeles.