The Omicron variant has caused havoc for airlines during the Christmas weekend, with over 1,000 flights canceled on Sunday and after thousands more were canceled on Friday and Saturday.

According to flight-tracking site FlightAware, flights from Delta, United and JetBlue have seen over 2,000 flights either delayed or canceled since Friday. On Sunday, there were 1,002 total cancellations within, into, or out of the U.S. and 3,475 delays.

The airlines have cited a shortage of crew members.

As of Sunday at 3:38 p.m. ET, Delta had canceled 140 flights, or 5%, for the day. JetBlue had canceled 112 flights, or 10%, while United canceled 103 flights, or 3%.

“Like many businesses and organizations, we have seen an increasing number of sick calls from Omicron,” JetBlue spokesperson Derek Dombrowski said in a statement. “Despite our best efforts, we’ve had to cancel a number of flights, and additional flight cancellations and other delays remain a possibility as we see more Omicron community spread.”

Southwest Airlines said their cancellations were caused entirely by weather and not issues related to COVID.

The New York Times noted Sunday that the number of Christmas Eve and Christmas Day travelers were nearly double from 2020.

Appearing Sunday on ABC News' "This Week," infection expert Dr. Anthony Fauci warned that new Omicron variant cases are likely to climb "much higher."