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United will require flight attendants to wear cloth face coverings or masks while they’re on duty starting April 24, according to an employee memo the airline shared with CNN.

United says it’s the first major US carrier to adopt the requirement.

The airline will not replenish the supply after every flight and rather, it will do so “as needed and as supplies permit,” the airline said in the memo.

Flight attendants also will have the option to wear their own face coverings or use the ones United provides.

United noted that the requirement “is in line” with Centers for Disease Control and Prevention recommendations that people wear cloth face coverings in public when social distancing isn’t possible.

The airline made the decision in partnership with the Association of Flight Attendants, according to the memo.