(NewsNation Now) — Confusion over U.S. flight cancelations continued Monday as a storm system in the Pacific Northwest further complicated a situation made difficult by the omicron variant, changing schedules and drawing down staffing levels at some carriers during the busy holiday travel season.

As of Monday night, 3,105 flights had been canceled and 14,239 delayed.

Alaska Airlines reported 165 cancellations Monday, the highest number of cancellations reported for a U.S.-based airline so far. Delta reported 118 cancellations, JetBlue has canceled 70 flights, United reported 99 flight cancellations and American Airlines reported 88 flight cancellations or 3% of its scheduled flights for the day so far, according to a running tally on the flight-tracking website FlightAware.com.

More than 1,500 flights into, out of, or within the U.S. were canceled Sunday, including more than 100 on major carriers.

On the day after Christmas, 817 flights were canceled within, into, or out of the United States by 12 p.m. CST, according to FlightAware.com.

TSA officers screened 1,533,398 people at airport security checkpoints nationwide Christmas day.

On Christmas Day, 955 flights were canceled, according to FlightAware.com. Delta, United and Jet Blue had canceled more than 10% of their Saturday scheduled flights.

In a statement shared with Nexstar, Delta said, “Delta teams have exhausted all options and resources, including rerouting and substitutions of aircraft and crews to cover scheduled flying. … We apologize to our customers for the delay in their holiday travel plans. Delta people are working hard to get them to where they need to be as quickly and as safely as possible on the next available flight.”

“The nationwide spike in Omicron cases this week has had a direct impact on our flight crews and the people who run our operation. As a result, we’ve unfortunately had to cancel some flights and are notifying impacted customers in advance of them coming to the airport,” United said Thursday.

American spokesperson Derek Walls said the cancellations stemmed from “COVID-related sick calls,” and the airline contacted customers Friday. 

Not all airlines said COVID-19 was disrupting their travel schedules. Southwest Airlines reported that “things are running smoothly.”

European and Australian airlines have also canceled holiday-season flights due to staffing problems tied to COVID-19. In addition, to ease staffing shortages, countries including Spain and the U.K. have reduced the length of COVID-19 quarantines by letting people return to work sooner after testing positive or being exposed to the virus.

Further exacerbating the situation are the long waits on hold for travelers calling airlines for updated information. Some airlines have suggested that monitoring and messaging through Facebook, Twitter and Instagram may be more effective and efficient than using the phone, as teams independent of phone banks are dedicated to keeping up with social media traffic.

Flight delays and cancellations tied to staffing shortages have been a regular problem for the U.S. airline industry this year. Airlines encouraged workers to quit in 2020, when air travel collapsed, and were caught short-staffed this year as travel recovered.

COVID-19 infections have surged in the United States in recent days due to the highly transmissible omicron variant, which was first detected in November and is now the dominant strain.

Travel problems this holiday season go beyond the airlines, with cruise lines also hit. The Centers for Disease Control and Prevention is investigating nearly 70 cruise ships with COVID-19 cases on board. A total of 55 fully vaccinated passengers and crew members on Royal Caribbean’s Odyssey of the Seas tested positive for COVID-19 and several ships have been turned away from ports because of onboard outbreaks.

The Biden administration will lift travel restrictions next week on eight southern African countries imposed last month over concerns about the omicron variant, the White House said Friday.