"Wearing a mask is among the simplest and most effective actions we can take to reduce transmission," said Delta CEO Ed Bastian.
One passenger is heard saying "she is in her face, oh Lord," in video footage of the heated dispute.
The International Air Transport Association found that most documented cases linked to air travel were diagnosed before airlines implemented mask mandates.
"Delta requires masks on every flight for the safety of our customers and crew," said an airline spokeswoman.
Delta, United, JetBlue and American Airlines are among the major carriers offering refunds to passengers who are refused boarding.
"We have already banned some passengers from future travel on Delta for refusing to wear masks on board," a Delta Airlines internal memo stated.
The airline is looking to have all 90,000 of its employees to be tested.
Billionaire investor Warren Buffett's company sold off stocks in four major U.S. airlines. During an annual meeting Saturday through a live-stream, he called the investments during a pandemic "a mistake."
American Airlines and British Airways have suspended certain international flights.
Representative Rashida Tlaib was detained with members of the labor union Unite Here Friday in a protest against Delta Airlines at Detroit Metropolitan Airport. "We won't stop until we get #fairwages and #healthcare," Tlaib tweeted.
"Sad to see that my preferred airline, @Delta flight 1998 has provisions for various languages and audio description for in-flight entertainment but no closed captions for deaf and hard of hearing flyers," the Academy Award winner tweeted Friday.
"If it had hit us, we would have been dead—it's that heavy," the man's neighbor said.
Passengers claim Delta Airlines have edited out references to homosexuality from the version of Elton John biopic "Rocketman" shown on their flights. It's one of several similar claims.
"We started dropping in altitude and then the oxygen masks dropped from the top of the plane, chaos sort of ensued amongst the passengers," one of the passengers said.
"I'm deeply hurt and offended that someone felt the entitlement to ruin and tamper with personal property with hate speech," said Renee Gerrish.
"I didn't know what was going on."
Former "Real Housewives of Atlanta" star was traveling home to Atlanta when she alleged Delta Airlines forced her family off of a flight when her husband Kroy Biermann arrived at the departure gate late.
"I thought it was a terrorist attack," said one passenger aboard the Delta flight, where a man announced he was God and that he "came to save the world!"
The pilot initially called for an emergency landing after the passenger attempted to open the door during the flight.
A photo of a poster that discourages Delta employees to join the union has gone viral for its argument that union fees would be better spent on video games.
Delany Luh said the experience left her feeling "humiliated, violated, scared and filled with anxiety."
"She became agitated and said, 'If you're gonna act like that we can go back to the gate and you can get off.' I held up my phone to show her that airplane mode was on."
"The safety and security of Delta people and our customers is always our top priority. We will always review and enhance our policies and procedures to ensure that Delta remains a leader in safety."
One person was taken to hospital.
The passenger reportedly approached the air marshal from behind and jumped on his back.