The US has opened an investigation into Delta Airlines as problems continue to plague the company five days after it was hit in a global IT outage.
Transportation Secretary Pete Buttigieg said Delta must provide passengers with refunds and other compensation for disrupted travel as required by law.
A day earlier, Delta, which has cancelled more than 5,000 flights since Friday, signalled it could take several more days for its operations to recover from the outage.
Meanwhile, CrowdStrike’s chief executive George Kurtz, whose cybersecurity firm sparked the chaos with a faulty overnight update, has also been called to testify in Congress.
The House Committee for Homeland Security said in a letter: “While we appreciate CrowdStrike’s response and coordination with stakeholders, we cannot ignore the magnitude of this incident.
It added: “Recognising that Americans will undoubtedly feel the lasting, real-world consequences of this incident, they deserve to know in detail how this incident happened and the mitigation steps CrowdStrike is taking.”
CrowdStrike said it was working on ways to make it easier and faster to fix the issue, which downed an estimated 8.5 million Microsoft Windows devices globally, hitting airlines, health systems and other services.
In many cases, IT teams had to reboot computers manually.
Delta, which appears to have had more difficulty recovering than other airlines, said that its crew-staffing system had been affected by the incident.
As of Tuesday morning, it had already cancelled more than 400 flights and delayed hundreds of others, following more than 1,150 cancellations a day earlier, according to tracking firm Flight Aware.
“All airline passengers have the right to be treated fairly, and I will make sure that right is upheld,” Mr Buttigieg wrote on social media.
“While you should first try to resolve issues directly with the airline, we want to hear from passengers who believe that Delta has not complied with USDOT-enforced passenger protection requirements during the recent travel disruptions. We will follow up.”
The Biden administration in April finalised a rule requiring that airlines promptly and automatically refund passengers for significant changes to their travel, and other issues.
It is part of a broader effort to step up policing of airlines after a series of major travel meltdowns.
Last year, Southwest Airlines agreed to pay $140m (£108m) resolve a Department of Transportation investigation launched after a storm disrupted service and set off a cascade of cancellations during the busy 2022 holiday travel period.