LIBERTY, Mo. — Although authorities have been encouraging people to wear masks to slow the spread of the coronavirus, many police departments leave it up to officers to decide whether to cover their faces while interacting with the public.

Some cities, including Chicago, Los Angeles and New York, require police to wear masks in most situations, but law enforcement officers elsewhere are exempt from such protocols.

In Kansas City, Missouri, two speakers at a Police Board of Commissioners meeting earlier this month criticized officers for routinely not wearing masks in public, saying they even had to hand out masks to some at that event.

At the time, the city exempted essential workers such as police officers and first responders from wearing masks, while requiring everyone else to do so outside the home. But Mayor Quinton Lucas removed that exemption on Monday as he issued a series of stricter guidelines citing a surge in COVID-19 cases.

The Centers for Disease Control and Prevention says masks help slow the spread of the coronavirus by inhibiting the flow of respiratory droplets that carry the virus. The CDC guidelines for law enforcement officers essentially mirrors safety guidance for members of the public.

In Minnesota, residents are required to wear masks in indoor businesses or public spaces, and people working outside must wear them when social distancing is not possible.

But police and other first responders have been exempt "in situations where wearing a face covering would seriously interfere in the performance of their public safety responsibilities."

Jim Mortenson, executive director for the Law Enforcement Labor Services, a Minnesota police union, said reasonable exemptions are necessary.

"If you come across somebody and someone starts firing a weapon on your vehicle as you're coming up on a scene, the last thing you are going to think about is putting a mask on," Mortensen said.

Other police union officials either declined to discuss the issue or said local police departments should take the lead on masking decisions. Mik Shanks, president of the Kansas State Lodge of the Fraternal Order of Police, said individual departments must determine how the officers are equipped.

It's reasonable to expect police to wear masks during more routine work, said David A. Harris, a law professor and expert on police issues at the University of Pittsburgh.

"When the requirement says they don't have to, period, it is understandable the public is going to ask why," Harris said. "If there's not a reason they can't and shouldn't wear masks, why not wear them?"

Mayors in New York and Chicago have said officers will be disciplined for not complying with mask ordinances following complaints from the public.

On Monday, when asked about unmasked officers at a recent demonstration, New York Mayor Bill de Blasio said his office has repeatedly talked to city agencies about the issue. He thinks progress has been made but that more needs to be done.

"Sometimes, particularly in public safety work or in health work, there may be a valid reason, but overwhelmingly, all public servants should have those masks on, period, and if they don't, there should be consequences," he said.

With COVID-19 cases on the rise in Chicago, Mayor Lori Lightfoot has threatened disciplinary action for officers who ignore a city requirement to wear masks on duty when social distancing is not possible.

The city has escalated its efforts to ensure officers comply, with department directives, public awareness campaigns, internal messaging and compliance checks. As of last week, disciplinary proceedings have begun against one officer for not wearing a mask, and other investigations are underway, city spokesman Howard Ludwig said.

The refusal to wear masks also is a symptom of low morale among police officers who have been repeatedly attacked and vilified, particularly since racial injustice protests erupted following the death of George Floyd in Minneapolis in May, said Eugene O'Donnell, a former New York City police officer and a professor at the John Jay College of Criminal Justice.

"You can't ignore that the culture war is central to this," O'Donnell said. "The government has kicked the stuffing out of police and used the issue as political mechanics. They have had no concern about the lives of officers, and they are seen as pretending to have concern with the mask issue. ... It's not a real good time to ask police for anything."

And it's unreasonable to expect officers to worry about wearing a mask while also carrying weapons and complying with other responsibilities, he said.

"It's game day out there. You have to take it seriously and tune in all the time," O'Donnell said. "Some officers legitimately just think adding to a long checklist of to-dos might be distractive to focusing on the job, which can quickly get serious."

Harris agreed that the masks can limit vision, hamper breathing and otherwise distract the officers. But while he sympathizes, he said following protocols that protect the safety of the public and other officers is part of the job.

"We're all fed up," Harris said. "Maybe they are more fed up than others. ... Masks are an inconvenience for everyone. This is more than misery loves company. They have signed up for a job that entails public contact. I'm sorry it's an extra thing, but those are the breaks."