WASHINGTON -- Three of the largest 4 US airlines said Thursday they would require passengers to wear facial coverings on US flights, joining JetBlue Airways Corp in taking the step to address the spread of the coronavirus and convince reluctant passengers to resume flying.

United Airlines, Delta Air Lines Inc and American Airlines Group Inc, along with the smaller Frontier Airlines, which is owned by private equity firm Indigo Partners LLC, announced they will require facial coverings next month.

Delta and United's new rules start May 4, while Frontier's start May 8 and American's requirements begin May 11. The policies exempt young children from wearing masks or other facial coverings.

Many US airlines are also requiring pilots and flight attendants to use facial coverings while on board aircraft.

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Airlines in the United States have seen a nearly 95-percent drop in US passengers and have slashed flight schedules. They are now working to reassure customers about the safety of air travel by instituting new cleaning and social distancing procedures.

Some airline unions and US lawmakers have urged the Federal Aviation Administration (FAA) to require facial coverings for all passengers and crew.

United said it would provide complimentary masks to passengers. Southwest Airlines Co, one of the largest US airlines, has not required facial coverings.

The FAA has declined to implement the requirement, and it is not clear if the agency has the authority to compel passengers to wear face masks. The FAA said Wednesday it was "working with air carriers to ensure they have processes in place for addressing public health risks for their crews and passengers."

Representative Peter DeFazio, who chairs the House Transportation Committee, called on the FAA Wednesday to "require masks or other face coverings for all crewmembers and passengers on US flights" and to require airlines "adopt reasonable, sound procedures for ensuring that passengers are spaced at safe distances from one another."

Delta said the airline will require face coverings "starting in the check-in lobby" and at "Delta Sky Clubs, boarding gate areas, jet bridges and on board the aircraft for the duration of the flight – except during meal service."

Delta added their use "is also strongly encouraged in high-traffic areas, including security lines and restrooms. People unable to keep a face covering in place, including children, are exempt."

American said the rules will prioritize "customer and team member well-being."

German airline group Lufthansa also said this week it would require facial coverings for all passengers starting May 4.

Sara Nelson, international president of the Association of Flight Attendants union, praised the carriers adopting the requirements and added "absent federal action, we need every airline to require passengers wear face coverings to keep everyone safe in aviation."