The DOT's Office of Aviation Consumer Protection has opened an investigation into Delta's ongoing operational meltdown.
"We have made clear to Delta that they must take care of their passengers and honor their customer-service commitments," DOT secretary Pete Buttigieg said in a prepared statement. "This is not just the right thing to do, it's the law, and our department will leverage the full extent of our investigative and enforcement power to ensure the rights of Delta's passengers are upheld."
Delta has cancelled more than 5,400 mainline flights and delayed more than 7,700 following the July 19 CrowdStrike outage, which crashed the Microsoft Windows operating system that Delta uses on more than half of its worldwide IT systems.
There also has been widespread delays and cancellations of Delta Connection regional flights, although regional cancellations largely dwindled on Tuesday.
Amid the chaos, Delta flyers are encountering a variety of customer-service issues, including misplaced baggage, prolonged call center hold times, and overwhelmed and faltering digital rebooking tools.
Delta says it is fully cooperating with the DOT.
"We remain entirely focused on restoring our operation after cybersecurity vendor CrowdStrike's faulty Windows update rendered IT systems across the globe inoperable," the carrier said in an emailed statement. "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."
Delta hasn't said when it expects to have its operation back to normal. But it has said it will issue SkyMiles points or travel vouchers to impacted customers, with amounts based on affected travel. The airline also says it will reimburse customers who have incurred hotel, meal and ground transportation expenses while in transit.
Delta customers whose flights have been canceled or significantly delayed can also cancel their travel and request a refund at delta.com/refund.
The investigation is likely to be similar in nature to the one DOT conducted into Southwest following an operational meltdown during the 2022 holiday season that led to nearly 17,000 cancellations over 11 days.
The case concluded late last year with a consent decree that included $140 million in penalties for Southwest.