DENVER The Department of Justice on Thursday sued Denver over what the federal government claims is an unconstitutional mask ban targeting federal agents and other law enforcement officers.The city ordinance, which was signed i nto law earlier this year, bans federal immigration and other law enforcement officers from wearing face coverings while working in Denver and requires them to clearly identify themselves with a visible ID when operating within city limits. Under the law, federal agents who do not comply could be cited with a $999 fine by Denver police and face up to 300 days in jail.Watch Denver7s prior reporting on this city ordinance in the video below: Denver ban on masks for ICE agents, other law enforcement approved by city council in unanimous voteThe lawsuit, filed in U.S. District Court of Colorado against the City of Denver, Denver Mayor Mike Johnston, Denver City Attorney Miko Brown, and Denver Police Chief Ron Thomas, argues that complying with the law would endanger officers and reduce operational effectiveness by, among other things, subjecting them to doxxing, harassment, and threats to their physical safety.Imposing Denvers more rigid facialcovering and identification rules would strip federal officers of the flexibility to determine when and how to identify themselves during immigration enforcement operations, undermining both officer safety and operational effectiveness, the lawsuit states.The complaint also argues that Denvers mask ban puts agents' safety under threat because it allows the public to photograph or record them during enforcement operations something people have the right to do under the First Amendment and makes the case that disseminating agents' identities online could be used by members of organized crime and transnational criminal organizations in serious and potentially deadly ways.While such a scenario has yet to play out nationally, the lawsuit claims the families of two federal agents in the Denver metro area and Durango have already been doxxed and harassed after their images were posted online.The lawsuit further argues that Denvers mask ban is a violation of the federal governments Supremacy Clause, which dictates that federal law takes precedence when it conflicts with local or state laws. In its claim for relief, the DOJ asks the federal court to declare Denvers ordinance as invalid as applied to federal law enforcement officers, agents, or agencies and to permanently prohibit the city from enforcing its mask ban.In a statement shared on Instagram shortly after the city was served with the lawsuit, Mayor Johnston said his office would fight to the very end on this battle to make sure that every law enforcement officer, local or federal, that operates in Denver does not wear a mask (and) is easily identifiable to the public.We think law enforcement should be transparent and accountable. An officer should not only not wear a mask; they should have a badge, they should have a name, they should have a badge number that you can track, Johnston said, vowing the city would stand by the ordinance.Mask ban came in wake of increasing tensions between ICE, public Denver City Council member Flor Alvidrez, one of the sponsors of the ordinance, told Denver7 earlier this year the law was in response to constituents concerns about how to distinguish law enforcement officers from bad actors as President Donald Trump sought to ramp up his mass deportation campaign."I think this is critical. When someone is in their home and someone's knocking on their door and they have a mask and a gun, who's going to answer the door? Why would you?" said Alvidrez. "This is literally trying to find the bare minimum that we can do to help people have some sense of safety and security in our city."Just last month, The Associated Press reported that the U.S. Immigration and Customs Enforcements human resources division was making final job offers before preliminary vetting steps had been completed, including fingerprints, identity verification and credit checks, raising concerns about the new hires.The citys mask ban isnt the only step Denver has taken to protect Denver residents from what Johnston has described as federal overreach.Just days after signing the mask ban ordinance, Johnston also signed an executive order banning ICE from city-owned or city-controlled property.Watch Denver7s story on that executive order in the video player below: Denver mayor signs order banning ICE from city property, laying out measures to protect protestersMore recently, Denver sued to block the Trump administration from sending armed federal immigration enforcement agents to voting sites during this years midterm elections, claiming their presence would be a violation of federal law.Police chief, council members reluctant to address mask ban enforcement questionsDenver7 has repeatedly brought up concerns about how the city would enforce its ICE mask ban, given the U.S. Constitution enshrines the federal government with a Supremacy Clause. In response, Council member Alvidrez said the city has authority over public safety and the use of city resources, even if it cant change federal law itself.She told Denver7 previously that the law is not meant to target ICE agents but aims instead to reduce the risk of residents or other officers from encountering someone who may not be who they say they are.But Brian Pacelko, the president of the Denver Police Protection Association, told Denver7 earlier this year there are still many questions about enforcement issues the law does not address."What will happen if an officer does take enforcement action, and a federal agent then tries to arrest that officer for impeding their operation? What happens to them if they're charged with a crime? Is there an internal affairs process? Are they sent home? Are they suspended without pay?" asked Pacelko. "These are our main concerns with how these things are going to affect our officers and their well-being."When Denver7 took these questions to Alvidrez earlier this year, she was hesitant to provide a definitive answer."It will have to be a lot of investigation... what my conversations have been with police, is that they will be on scene if there is an imminent threat," Alvidrez said. "They will not be on scene if everything is being followed by the law. Their goal is never to interfere with federal supremacy. It's just holding bad actors accountable."A spokesperson for the Denver Police Department told Denver7 that when it came to enforcement, "of utmost importance is discretion and prioritizing de-escalation when encountering these situations. Our goal is to apply this ordinance in a way that builds trust and transparency without putting officers, deputies, or the public at risk."Though similar bans went into effect in places like Los Angeles, New York, Seattle, Chicago, Milwaukee and Philadelphia earlier this year, most have either been blocked by federal judges or are subject to pending litigation by the federal government. ...read more read less