DENVER (KDVR) — According to FlightAware, Southwest Airlines has canceled 158 flights into and out of Denver International Airport on Sunday.

Hundreds of passengers were left standing in line at DIA, hoping to figure out what they’ll do about delayed or missed trips to their destinations.

When asked if cancellations were the result of widespread Federal Aviation Administration air traffic staffing shortages, the FAA released this statement:

“No FAA air traffic staffing shortages have been reported since Friday. Flight delays and cancellations occurred for a few hours Friday afternoon due to widespread severe weather, military training, and limited staffing in one area of the Jacksonville Air Route Traffic Control Center. Some airlines continue to experience scheduling challenges due to aircraft and crews being out of place. Please contact the airlines for details about current flight schedules.”

Following another day of excessive cancellations and delays, Southwest responded with this statement explaining the ATC issues: “We experienced weather challenges in our Florida airports at the beginning of the weekend, challenges that were compounded by unexpected air traffic control issues in the same region, triggering delays and prompting significant cancellations for us beginning Friday evening. We’ve continued diligent work throughout the weekend to reset our operation with a focus on getting aircraft and Crews repositioned to take care of our Customers.

With fewer frequencies between cities in our current schedule, recovering during operational challenges is more difficult and prolonged.

We’re working diligently to accommodate our Customers as quickly as possible, and we are grateful for their patience. We’re offering Customers added flexibility to explore self-service rebooking options on Southwest.com, where they can get updates on the status of their travel. We know the frustration flight cancellations are creating for our Customers and Employees and we apologize, and we again thank everyone for patience as we work first to be safe, and second to be as quick as possible in solving disrupted plans.”

Southwest canceled 39 flights out and 57 flights into DIA on Saturday.

The company posted this statement on its Facebook page: “Air Traffic Control (ATC) issues and disruptive weather have resulted in a high volume of cancellations throughout the weekend while we work to recover our operation. We appreciate your patience as we accommodate affected Customers as quickly as possible, and Customer Service wait times are longer than usual. If your travel was affected, please explore self-service rebooking options by checking your flight status on southwest.com.“

One FOX31/Channel 2 viewer sent us an email that she learned on Friday night her flight out of Denver was canceled, then the rebooked flight on Saturday was canceled just before boarding.

Our Nexstar sister station in Las Vegas reported several Southwest flights were canceled in and out of McCarran International Airport and said the company cited weather and the ATC issues.

Southwest Airlines announced requiring all employees to get vaccinated against COVID-19 on Oct. 4. It is unclear if the increase of cancelations is related to the new mandate.

“Southwest Airlines must join our industry peers in complying with the federal government’s COVID-19 vaccination directive,” Gary Kelly, Southwest Airlines Chairman and CEO said. “I encourage all Southwest Employees to meet the federal directive, as quickly as possible, since we value every individual and want to ensure job security for all.”

United Airlines and Frontier Airlines announced COVID-19 vaccination mandates for their employees two months ago, while American Airlines and JetBlue announced their mandates last week.