Total flight cancellations within, into, or out of the United States as of 6.07 am ET were 669, as per flight-tracking website Flightaware.com https://uk.flightaware.com/live/cancelled/today. Nearly 860 flights were canceled on Sunday.

Delta Air Lines, United Airlines Holdings Inc and Republic Airlines Inc had over 100 cancellations each, while American Airlines Group Inc canceled 51 flights as of early Monday.

The companies did not immediately respond to a request for comment.

In Europe, recent airport snarls have been blamed on a shortage of employees, as many workers, who were laid off during the pandemic, desert airport work for flexible working practices and other occupations.

Even the U.S. regulator Federal Aviation Administration (FAA) faces staff shortages.

The FAA last week granted United approval to temporarily cut Newark flights after the Chicago-based carrier petitioned for a waiver, citing airport construction and air traffic control staffing.

Airlines for America, a trade group, said on Friday the FAA must ensure adequate air traffic control staffing to avoid further summer travel disruptions.

(Reporting by Nathan Gomes in Bengaluru)