The parent company of Aer Lingus and British Airways has said it will operate at only 30% of its usual capacity in the final three months of 2020.
IAG said recent bookings had been lower than expected due to additional COVID-19 measures implemented by many European governments, including an increase in local lockdowns and the extension of quarantine requirements to travellers from an increasing number of countries.
The airline group also said governments had not moved as quickly as expected to implement measures such as pre-departure testing and air-corridor arrangements.
The airline industry has been pushing for such initiatives to replace quarantine periods and make customers more likely to travel.
The news came as IAG reported a €1.3 billion loss for the third quarter of this year as passenger traffic slumped by 88% compared with a year earlier, leading to an 83% drop in revenue.
The company does not now expect to break even in the final three months of the year.
The IAG figures come after Ryanair last week announced big cuts to its winter schedule.