(NewsNation) — A passenger is suing Southwest Airlines for failing to give him a refund after his family’s flights were canceled.

Southwest canceled thousands of flights after winter weather snarled air travel and the airline’s systems were unable to cope, leading the company to do a reset with fewer than half of its flights operating.

Passengers say the airline didn’t refund them or rebook them quickly, as it is mandated to do by law. The man who filed the proposed class action lawsuit said the airline only offered credits for the flights he and his daughter were meant to take.

Southwest said people booked on flights from Dec. 24 to Jan. 2 that were canceled or “significantly” delayed received the 25,000 points. It has not disclosed how many passengers were booked on those flights.

CEO Bob Jordan also wrote an apology letter released by the airline.

“I know that no amount of apologies can undo your experience,” Jordan wrote. He added the airline is acting “with great urgency” to process refunds, return lost bags and handle requests for reimbursement of costs incurred by stranded travelers.

The lawsuit says Southwest’s own customer service guidelines say it must give a refund to passengers whose flights were delayed or canceled.

Department of Transportation guidelines also state airlines must refund passengers for canceled or “significantly delayed” flights. Southwest is already being investigated by the DoT for the high rate of cancellations.

The Associated Press contributed to this report.