Complaints by U.S. airline passengers rose dramatically this spring as waves of flight delays and cancellations swept the industry.

There were 5,079 consumer complaints filed with the Department of Transportation in April, 15% above the prior month and more than four times the number in April 2019 before the pandemic, the agency reported Thursday.

The figures coincided with a jump in delays and cancellations in April as airlines struggled to handle increased, post-pandemic demand. Other factors, including bad weather and growing private flights, strained the air-traffic system.

There were 13,397 flight cancellations in April, a 47% increase from March, according to DOT data. A majority of the consumer complaints in April were on flight disruptions or disputes over refunds, the agency said. April is the most recent month for which there is data.

The report comes after Transportation Secretary Pete Buttigieg was forced last week to drive to New York from Washington after his flight was canceled. Buttigieg has been pressing airlines to adopt more reasonable schedules during the busy summer travel season.

The complaint statistics were earlier reported by Reuters.