Ryanair is cutting capacity by almost a fifth in the coming months.
The airline says forward bookings have "notably weakened" over the past 10 days, given uncertainty over COVID-19 rates in some EU countries.
Most of the cuts in September and October will be a reduction in frequency rather than route closures.
The airline says it is now contacting any impacted passengers by email.
In a statement, a Ryanair spokesperson said: "Over the past two weeks as a number of EU countries have raised travel restrictions, forward bookings especially for business travel into Sept & Oct have been negatively affected.
"It makes sense to reduce frequencies so that we tailor our capacity to demand over the next two months."
The company is calling on the Irish Government to add more European countries with lower or similar coronavirus rates to Ireland to the travel 'green list' - in particular the likes of Germany, the UK and Portugal.
Ryanair earlier this month said it restored 60% of its normal flight schedule for August.
