The low-cost carrier has canceled more than 20,000 flights.

Ryanair has canceled an additional 18,000 flights that will affect customers from November through March.

The low-cost airline has faced backlash after previously canceling more than 2,000 flights because of a lack of available pilots, and the additional cancelations bring the number of halted flights to more than 20,000, according to The Independent.

“While over 99 per cent of our 129 million customers will not have been affected by any cancellations or disruptions, we deeply regret any doubt we caused existing customers last week about Ryanair’s reliability, or the risk of further cancellations,” CEO Michael O'Leary said in a statement.

The latest wave of cancelations will affect 400,000 passengers, suspending 34 routes during the winter season. Ryanair is offering affected air travelers a refund or a rescheduled flight, as well as up to 80 euros (approximately $94) in vouchers.

Ryanair blamed the current lack of pilots on a mishandling of vacation requests. Experts have suggested that Norwegian Air has been poaching Ryanair's pilots.

The airline offered a sale with one-way fares for less than $15 for the winter, and it's unclear how many of those flights will be affected.