The warning comes as COVID-19 cases are on the rise in New York City, driven by an uptick in at least a dozen neighborhoods.
In an email Friday, officers were reminded "that they are required to wear face coverings at all times when performing duties in public areas, department facilities and whenever social distancing is not possible."
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The memo said officers can't wear face coverings "that were not originally designed for that purpose" including scarves, bandanas and handkerchiefs.
"It is our responsibility to set the example for our great city. And do everything we can to help ensure we do not have another hospitalized member bring this deadly infection into our homes, or have another funeral," Chief of Department Terence Monahan said in a video memo that was sent to all officers' phones.
Officers at police headquarters heard repeated messages over the building's loud speaker reminding them to wear face coverings.
Chief Monahan also announced that a memorial service will be held Monday morning at St. Patrick's Cathedral for the 46 NYPD officers who died of coronavirus.
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Select family members will be permitted to attend the service.
On Saturday the Health Department said it is tracking 4 concerning clusters of COVID-19 cases in Southern Brooklyn, Williamsburg, Central Queens and Far Rockaway.
They're among 12 neighborhoods in the city with positivity rates above 3%.
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