After flight attendants and pilots criticized them for not doing more to protect employees, large airlines in the United States and around the world announced this week that they would require their crews and passengers to wear masks.

American Airlines, Delta Air Lines and United Airlines all said on Thursday that they would start requiring all passengers to wear a face covering in the coming weeks, a policy that will apply to their flight attendants and some other workers, too. The three join Lufthansa Group — which owns its namesake airline, Swiss International Air Lines and Austrian Airlines — as well as JetBlue and Frontier Airlines, all of which made similar announcements this week. Southwest Airlines has said a policy for flight attendants is coming.

As some states begin to relax or lift stay-at-home orders, lawmakers and unions representing flight attendants and pilots have stepped up calls for industrywide rules on masks to protect flight crews from passengers — and passengers from one another.

Airlines have been slow to require masks in part because they’ve been hard to come by. Early in the pandemic, many companies promised to make masks available for employees who wanted them, but some pilots and flight attendants complained that they were not always available.