• The U.S. Department of Transportation's Office of Aviation Consumer Protection is investigating Delta Air Lines over chaos sparked by last week's global IT outage, according to a statement.
• The DOT cited widespread flight disruptions and customer service failures in which Delta did not uphold commitments to its passengers, it said.
• Last week a software update from CrowdStrike led to a historic outage of Microsoft systems. Airlines and other global industries were roiled, with Delta Air Lines hit particularly hard.

The U.S. Department of Transportation said it is investigating Delta Air Lines over thousands of flight cancellations in the wake of Friday's IT outage.

The DOT cited widespread flight disruptions and customer service failures in which Delta did not uphold commitments to its passengers, it said. The agency also said the investigation will evolve as the DOT processes a "high volume" of customer complaints.

"Our department will leverage the full extent of our investigative and enforcement power to ensure the rights of Delta's passengers are upheld," Transportation Secretary Pete Buttigieg said.

Delta acknowledged the department's notice of investigation and said in an emailed statement it is fully cooperating.

"Across our operation, Delta teams are working tirelessly to care for and make it right for customers impacted by delays and cancellations as we work to restore the reliable, on-time service they have come to expect from Delta," the carrier said.

Last week a software update from CrowdStrike led to a historic outage of Microsoft systems. Airlines and other global industries were roiled, with Delta Air Lines hit particularly hard.

Delta CEO Ed Bastian in a video message to employees Monday called it "a horrible weekend" and said the airline had canceled more than 4,000 flights since Friday.

Delta Chief Information Officer Rahul Samant said in the message to staff that while the carrier has been able to restore most of its systems, the "critical" crew tracker is not yet up and running. That outage has left many crew members in limbo.

"I know many of you were stranded over the weekend or trying to get to work while flight after flight was canceled. I share your frustration in seeing passengers stranded while we, as crew members, experience the same unacceptable obstacles we face during every [irregular operation] — the inability to contact the Company in any capacity and the feeling that we have been abandoned in the system," said Darren Hartmann, a Delta captain and chairman of the airline's chapter of the Air Line Pilots Association, the pilots' union, in a message to crews.

Delta executives warned the challenges would persist into this week — during the busy summer travel season.

On Tuesday, 12% of Delta flights were canceled and 13% were delayed as of midmorning, according to FlightAware, with some passengers still stranded in airports even days after the outage.

Social media users have been sharing photos and videos of jam-packed airports, including in Atlanta and Minneapolis, claiming some people have been stuck there for multiple days, faced with an overwhelming demand for rental cars and hotels.

The event has drawn comparisons to Southwest Airlines' crisis of 2022 in which it canceled 16,900 flights, stranding more than 2 million passengers due to operational failures over the Christmas and New Year holidays.

The DOT penalized Southwest $140 million, a sum 30 times larger than any previous consumer protection violations penalty from the department.

Bastian said in his internal message that he had spoken to Buttigieg on Sunday about Delta's commitment to its customers and said, "We do our very best, particularly in tough times taking care of our customers."