United Airlines and Delta Air Lines have jointly cancelled more than 200 flights on Christmas Eve. The airlines give the omicron variant as the reason, which has caused infections among many crew members.
Thousands of planes fly over the United States every day, but the cancellations will still leave travellers stranded at the last minute.
Delta CEO Ed Bastian earlier this week proposed to the US health service CDC shorten the mandatory quarantine for fully vaccinated people from 10 to 5 days after infection.
That would ensure that fewer staff have to stay at home.