The US Department of Transportation (DOT) has launched an investigation into Delta Air Lines as it struggles to get its systems back up following the global CrowdStrike tech outage last week.

In a post on X (formerly Twitter), DOT Secretary Pete Buttigieg said the investigation aims to "ensure the airline is following the law and taking care of its passengers" despite a widespread disruption.

"All airline passengers have the right to be treated fairly and I will make sure that right is upheld," he wrote.

The investigation comes after Buttigieg revealed that the DOT received hundreds of complaints about Delta over "unacceptable customer service conditions" and continued disruptions.

"I have made clear to Delta that we will hold them to all applicable passenger protections," Buttigieg said in Sunday's post. "Delta must provide prompt refunds to consumers who choose not to take rebooking, free rebooking for those who do, and timely reimbursements for food and hotel stays to consumers affected by these delays and cancellations, as well as adequate customer service assistance."

In a statement to Fox Business, Delta said it is fully cooperating with the transportation department in the investigation.

READ ALSO: Delta Continues Flight Cancellations Days After Global IT Outage, Amounting to $163 Million Loss

What Happened to Delta Air Lines?

Last week, a faulty security update from Crowdstrike led to a global tech outage, causing many computers running Microsoft Windows to display the "blue screen of death." The disruption led to the cancellation or delay of thousands of flights across the world.

Most businesses impacted by the outage have regained their systems and resumed regular operations. However, Delta continued to struggle, canceling 478 flights as of 7:57 pm Eastern Time on Tuesday. The airline has also delayed 1,453 flights, according to data from flight tracker FlightAware. Delta has far exceeded cancellations by any other US airline.

In a statement posted on its website, Delta said it is focusing on restoring its operations. It also noted that more than half of its systems are Windows-based and required manual repairing and rebooting following the tech outage. The company also said each system requires additional time to synchronize.

Delta said it is extending its travel waiver for all customers with trips booked from July 19 to July 28.

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