Airbus has issued an urgent directive to perform software updates on more than 6,000 A320 aircraft worldwide, disrupting air travel as airlines were forced to ground a significant portion of their fleets during one of the busiest travel periods of the year.

The move, described by CNBC as one of the largest in Airbus’ history, quickly affected holiday flights in the United States and spread to Asia and Australia, where many carriers rely on A320s for short-haul routes.