United Airlines is the latest carrier to insist that all passengers wear face coverings when travelling with the airline.
The airline has now gone one step further in requiring passengers to do the same, starting from May 4.
United said that it would provide face masks free of charge to all customers, as part of a raft of measures designed to keep customers and employees safe.
Last month the carrier implemented social distancing on its flights, including restricting advanced seat selection for adjacent seats in all cabins, and boarding fewer customers at a time to allow for more distance during the boarding process.
For a round-up of which carriers are introducing face masks for staff and passengers, see: