Southwest Airlines is slated to undergo another round of federal scrutiny after the airline’s holiday meltdown that caused the carrier to cancel over 70 percent of its flights the day after Christmas.

Senate Commerce, Science and Transportation Chair Maria Cantwell, D-Wash., announced Wednesday night the panel will hold hearings on Southwest’s “massive operational and customer service failures” as a part of the upcoming Federal Aviation Administration reauthorization bill discussions. The announcement adds another layer of scrutiny to a Transportation Department probe promised during the holiday flight chaos.

“Southwest’s customers are rightfully dissatisfied and deserve better,” Cantwell said in a statement. “These consumers need refunds and reimbursements for their expenses.”

Cantwell added that she has spoken with Southwest CEO Bob Jordan as well as DOT Secretary Pete Buttigieg about the situation and intends to focus on strengthening consumer protections and airline operations.

Federal investigations have singled out Southwest Airlines due to the carrier’s disproportionate cancellations and delays following a massive snowstorm over the holiday weekend. Although passengers were told to expect delays following the storm, Southwest was the only airline to suffer cancellation rates well above 50 percent in the days around Christmas, according to FlightAware data at the time. The carrier still blamed the severe weather for its operational issues, adding in a Dec. 27 statement that it was “fully staffed and prepared for the approaching holiday weekend.”

Other airlines, including American, United, Delta and JetBlue, had about a 2 percent cancellation rate by Dec. 27.

Disgruntled Southwest passengers flooded social media with videos and stories of flight crews not showing up for rebooked flights, luggage becoming stranded in different airports and receiving few or no answers from its customer service personnel — if they were able to get through to them. Some passengers reported waiting five or more hours on Southwest’s customer service hotline.

Southwest had to reduce its schedule by one-third to handle the situation, causing more chaos for passengers with cancellations scrambling to rebook their flights. The airline resumed normal operations on Dec. 30.

Customer service

DOT announced on Twitter on Dec. 26 that it intended to investigate whether Southwest was following its customer service plan, which outlines the carrier’s reimbursement plan. According to the plan, the airline will offer meal vouchers for flight delays for over three hours that are in the airline’s control. For delays not in its control, “we will rebook you on the next available Southwest flight  …  at no additional cost” or refund the ticket.

Rep. Rick Larsen, D-Wash., whom Democrats recently elected ranking member of the House Transportation and Infrastructure Committee, said in a tweet Dec. 27 that Southwest told him it will deem all cancellations as of Dec. 24 as “controllable,” “meaning reimbursement for incidental expenses,” Larsen wrote. That same day, Buttigieg also met with union leaders and Jordan “to convey the Department’s expectation that Southwest meet its obligations to passengers and workers and take steps to prevent a situation like this from happening again.”

Larsen added he also will speak with Southwest pilots, flight attendants and customers about how to minimize disruptions in the future.

DOT has already stepped up enforcement actions surrounding flight refunds. In November, the department announced enforcement actions that mandated six airlines, including Frontier, to refund more than $600 million to their customers. Southwest, however, was not one of the six airlines.

The department is also in the process of reviewing a proposed rule that would require airlines to more clearly define under which circumstances passengers will receive refunds as well as issue refunds instead of non-expiring travel credits or vouchers if passengers cannot fly due to a communicable disease. The comment period for the proposed rule closed Dec. 16.

Cantwell and Sens. Edward J. Markey, D-Mass., and Richard Blumenthal, D-Conn., filed comments under the rule calling for DOT to ensure airlines cover secondary costs, like hotels, as well as report refunds and vouchers to the Bureau of Transportation Statistics monthly.

Although it’s not clear what kind of provisions Cantwell would support adding to the FAA reauthorization bill, she pushed for the updated consumer refund rule in a Dec. 27 statement, adding that “many airlines fail to adequately communicate with consumers during flight cancellations.”

Southwest Airlines said that it has received notice of the hearings from Cantwell’s office and will “remain engaged with our partners on Capitol Hill.”