Editor’s Note: This story has been updated to include a statement from Delta Air Lines.

(NEXSTAR) – Two major airlines have canceled dozens of flights scheduled for Christmas Eve, largely due to the omicron variant.

United Airlines has canceled about 120 flights scheduled for Christmas Eve due to COVID-19 cases impacting staffing.

The company shared a statement with Nexstar saying, “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. We’re sorry for the disruption and are working hard to rebook as many people as possible and get them on their way for the holidays.”

According to FlightAware, a flight-tracking service, United has canceled 121 flights as of 7:30 p.m. ET Thursday. While United has not yet confirmed whether COVID’s impact on staffing will affect flights on Christmas, FlightAware shows about two dozen of the airline’s flights have been canceled for Saturday.

FlightAware is also reporting Delta Air Lines has canceled over six dozen flights scheduled for Christmas Eve. In a statement shared with Nexstar, the company says “Delta teams have exhausted all options and resources — including rerouting and substitutions of aircraft and crews to cover scheduled flying — before canceling around 90 flights for Friday. 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.”

A spokesperson says the cancelations are due to a number of issues, including potential inclement weather and the impact of the omicron variant.

Omicron recently became the dominant COVID variant in the U.S. As of Thursday, the U.S. has surpassed its summer peak of COVID infections with a seven-day average of more than 168,000 cases, according to data from The New York Times.

Last week, the president of the nation’s largest flight attendant union and executives at United Airlines, American Airlines, Southwest Airlines, and Delta Air Lines testified during a Senate Commerce Committee hearing on airline oversight. During the hearing, Southwest Airlines CEO Gary Kelly told the Senate panel that the air in passenger jets’ cabins is so clean that face masks “don’t add much” additional protection against the spread of COVID-19 on planes, The Hill reports. Kelly tested positive for COVID-19 days after the hearing.