"We believe this change will give customers and employees some additional comfort when traveling with us," said Delta chief customer experience officer Bill Lentsch in a written statement.
Children and others who can’t keep a face covering in place will be exempt.
Delta earlier this week began requiring employees who come within six feet of customers or co-workers to wear masks and encouraged customers to wear masks.
JetBlue Airways announced earlier this week it will require customers to wear masks starting May 4, and Frontier Airlines on Thursday morning announced a mask requirement for passengers effective May 8.
American Airlines also announced Thursday afternoon it will require customers to wear a face mask starting May 11, and United Airlines said Thursday evening it will require travelers to wear face coverings starting May 4.
Southwest Airlines said Friday it would require customers to wear face masks starting May 11. Industry group Airlines for America late Thursday said its members will require employees and passengers to wear masks.
Frontier is also requiring passengers to certify before checking in on the airline's website or mobile app that neither they nor anyone in their household have had COVID-19 symptoms in the last 14 days, and to confirm that they they will check their temperature before heading to the airport and not travel if they have a fever.
U.S. Rep. Peter DeFazio of Oregon, the Democratic chairman of the House transportation committee, this week urged the Federal Aviation Administration to require crews and passengers to wear masks.
According to a statement from the FAA, the agency's administrator Steve Dickson, a former Delta executive, expects airlines to follow guidance from the U.S. Centers for Disease Control and Prevention, including its guidance on use of masks.
The FAA said its responsibility is to promote the safe operation of aircraft, and it is not a public health agency but “is working with air carriers to ensure they have processes in place for addressing public health risks for their crews and passengers.”
The Association of Flight Attendants, a union that represents flight attendants at United and other airlines, has called for airlines to require passengers to wear face coverings, absent a federal requirement.