Fifteen senators, including Bernie Sanders, Elizabeth Warren and Cory Booker, sent a letter to Southwest CEO Bob Jordan on Friday demanding answers about the airline’s management of 2022 holiday travel disruptions, which left thousands of passengers stranded in airports.

The questions push for details about the causes of the meltdown, including Southwest’s outdated software and staffing failures. The mass cancellations came alongside an intense snowstorm and elevated holiday travel demand, which posed a challenge to many airlines.

However, Southwest’s cancellations were uniquely outsized.

“Although winter storm Elliott disrupted flights across the country, every other airline operating in the United States managed to return to a regular flight schedule shortly thereafter — except Southwest,” the letter reads.

The airline canceled nearly 17,000 flights between Christmas Eve and New Year’s Eve. The company projected that the meltdown would cost it between $725 million and $825 million in the fourth quarter.

The senators also asked the airline for details on compensating affected passengers via ticket refunds, returning lost baggage and reimbursements for alternate travel arrangements made in the wake of Southwest cancellations.

Southwest is still in the process of reviewing requests for reimbursement and refunds from impacted customers.

The senators’ letter also highlights Southwest’s use of funds, claiming it neglected to update company-wide systems that have long been out of date.

“Southwest has long known that its software was outdated, and the Southwest Airlines Pilots Association had warned that such a debacle was inevitable unless Southwest invested in new scheduling systems,” the letter says. “Instead of making those investments, Southwest distributed over $1.8 billion in dividends to its shareholders and bought back over $11 billion in its shares between 2011 and 2020.”

Sen. Sanders previously bashed Southwest on Twitter for its “corporate greed,” noting that the airline used $5.6 billion of its $7 billion in Covid relief on stock buybacks for shareholders rather than invest in its internal infrastructure.

The senators are giving Jordan until Feb. 2 to respond to their questions.