Delta canceled another 400 flights Tuesday as its troubles in the wake of the global CrowdStrike-Microsoft IT outage dragged on for the fifth consecutive day.

The Atlanta-based carrier also saw more than 300 flights delayed Tuesday.

The ongoing issues have prompted the U.S. Department of Transportation’s Office of Aviation Consumer Protection to open an inquiry into Delta, citing “the high volume of consumer complaints” it has received about issues at the carrier.

“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 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 been uniquely affected by the global IT outage compared with other major carriers, who have since largely resumed normal operations. In a statement on its website Monday afternoon, Delta estimated that more than half of its IT systems worldwide rely on Microsoft Windows.

Friday’s CrowdStrike error, it said, ‘required Delta’s IT teams to manually repair and reboot each of the affected systems, with additional time then needed for applications to synchronize and start communicating with each other.’

It continued: ‘One of Delta’s most critical systems — which ensures all flights have a full crew in the right place at the right time — is deeply complex and is requiring the most time and manual support to synchronize,’ it said.

A Delta representative did not immediately respond to a request for comment Tuesday.   

Social media has been filled with images of passengers stranded away from their destinations. An additional complicating factor has been coordinating flyers’ luggage as they seek to rebook, reflected in a significant volume of Delta’s social media team responses on X related to baggage issues.

In a video message to employees on Monday, CEO Ed Bastian and Chief information Officer Rahul Samant provided an update on the situation.

Bastian said the company is working around the clock to get its operation back on track, but it will take another couple of days before the worst is over.

“Today will be a better day than yesterday and hopefully Tuesday and Wednesday will be that much better again,” he said.