Passengers are seen wearing protective masks and gloves at Miami International Airport in Miami, Florida, United States on March 29, 2020.

Major U.S. airlines on Thursday said they will require travelers to wear face masks on board their planes as carriers take steps to try to protect the health of passengers and crew.

Delta's policy requires travelers to wear a mask or other face covering in the check-in area, premium lounges, boarding gate areas and on board for the whole flight, except during meals. The airline is also urging travelers to wear them in security lines and in restrooms. The policy takes effect Monday.

United will also start requiring masks for passengers Monday. American's policy goes into effect May 11. Frontier Airlines issued a similar requirement that goes into effect May 8. JetBlue Airways earlier this week became the first major U.S. airline to mandate masks for travelers.