NEW YORK (Associated Press) – Airlines canceled hundreds more flights Saturday because of staffing issues tied to COVID-19, disrupting holiday celebrations during one of the busiest travel times of the year.

Flight-tracking website FlightAware notes nearly 1,000 flights entering, leaving or inside the U.S. were canceled Saturday, up from 690 scrapped flights Friday.

Over 250 more flights were already canceled for Sunday. FlightAware does not say why flights are canceled.

Delta, United and JetBlue on Friday had all said the omicron variant was causing staffing problems leading to flight cancellations.

Flight delays and cancellations tied to staffing shortages have been a regular problem for the U.S. airline industry this year.