By David Shepardson

(Reuters) – United Airlines (NYSE:) and Delta Air Lines(NYSE:) announced Thursday that they each had canceled dozens Christmas Eve flights. This was due to the COVID-19 Omicron variant spreading, which is putting a strain on their flight crews.

Chicago’s United cancelled 120 flights on Friday while Atlanta’s Delta claimed it had canceled approximately 90. Both airlines said that they are working with passengers to ensure they don’t get stuck at airports.

“The Omicron spike across the country this week has directly affected our flight crews, and those running our operation,” United said. 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.

Delta stated that it had exhausted all possibilities and resources, including the rerouting of crews and aircraft to meet scheduled flying. It then cancelled around 90 flights on Friday.

Delta mentioned potential inclement conditions and the Omicron variant’s impact for cancellations.

Delta Chief Executive Ed Bastian requested that the U.S. Centers for Disease Control and Prevention (CDC), reduce the quarantine guidelines for people who have had breakthrough COVID-19 infected, citing its impact on carrier workers. Bastian demanded that the quarantine period for those who have COVID-19 infections be increased to five days, instead of the 10.

This request was echoed by both Airlines for America (a trade group that represents major cargo and passenger carrier carriers), which sent a letter to the CDC Thursday and JetBlue Wednesday.

Updated quarantine guidance was released by the CDC for healthcare workers Thursday. It reduces isolation to seven days for those who have tested positive for COVID-19 and are not symptomatic.