The Transportation Department announced it will investigate Southwest Airlines’ onslaught of cancellations that stranded hundreds of travelers and their luggage at airports and wreaked havoc on holiday plans.

Although passengers were told to expect cancellations and delays after a weekend snowstorm swept through the country, Southwest canceled more than 70 percent of its flights on Monday and 60 percent on Tuesday, according to flight tracker FlightAware. Other airlines, including American, United, Delta and JetBlue, had only about a 2 percent cancellation rate by Tuesday.

The massive and disproportionate delays triggered scrutiny from the Transportation Department, which tweeted Monday night that the agency intends to “examine whether cancellations were controllable and if Southwest is complying with its customer service plan.”

“USDOT is concerned by Southwest’s unacceptable rate of cancellations and delays & reports of lack of prompt customer service,” the department tweeted.

Twitter has been flooded with tweets from Southwest passengers detailing ongoing flight delays, cancellations, baggage loss and more as the airline struggles to recoup from the weekend storm. Although airlines had canceled as many as 20 percent of flights over the weekend due to concerns about intense snowfall, Southwest appeared to be the only airline still struggling to keep flights on schedule.

One tweet shows hundreds of checked “stranded” bags lined up around baggage carousels in a Tampa, Fla., airport. The airline has reportedly been sending bags to their final destination even if the flight has been canceled. Another tweet noted Southwest’s check-in line in a Milwaukee airport, where one woman had been waiting for five hours. Another said she had been on hold with the airline’s customer service line for six hours.

Although some passengers have received vouchers for their canceled flights, other passengers have claimed they have not been offered any compensation or vouchers. Southwest’s customer service plan details that 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.

Southwest has in part been blaming the weekend storm for its cancellations, which might characterize some flight issues as “out of its control.” But passengers have complained that flight crews have not shown up to their rebooked flights, which could constitute a situation in the airline’s control.

Southwest said in a statement Monday that it was “fully staffed and prepared for the approaching holiday weekend when the severe weather swept across the continent,” adding that “these operational conditions forced daily changes to our flight schedule at a volume and magnitude that still has the tools our teams use to recover the airline operating at capacity.”

“As we continue the work to recover our operation, we have made the decision to continue operating a reduced schedule by flying roughly one-third of our schedule for the next several days,” it continued. “With no concern higher than ultimate safety, the people of Southwest share a goal to take care of each and every Customer. We recognize falling short and sincerely apologize.”