Frontier Airlines is the latest air carrier to require its passengers to wear face masks.
JetBlue made a similar announcement Monday, The Denver Post reported.
Starting May 8, passengers checking in for flights at the ticket counter, waiting at gates and those on the planes will all be required to wear masks that cover their mouths and noses.
Flight crews have already been required to wear a mask since April 13, the Post reported.
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Passengers also have to sign a paper saying they are healthy enough to travel, KDVR reported.
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They have to certify that they and no one in their home had any COVID-19 symptoms in the previous 14 days, they will check their temperature before heading to the airport, staying home if they have a fever and they will wash their hands/sanitize before getting on the plane, according to KDVR.
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Frontier is also disinfecting its planes, mixing fresh and recirculated air that is passed through high-efficiency particulate air filters and blocking every other row to enforce social distancing, KDVR reported.