Belgium has said it intends to take Ryanair to court, accusing it of illegally punishing customers hit by thousands of flight cancellations.
Belgian Deputy Prime Minister Kris Peeters, who handles the consumer affairs portfolio, said in a statement that the airline has "shown a lack of professionalism".
Mr Peeters accused Ryanair of a series of failings, including only communicating with Belgium's French and Dutch-speaking customers in English and a failure to notify them of their rights.
Ryanair said it complies fully with all EU261 legislation and is taking all necessary steps to re-accommodate affected customers.
He added that he has "lodged a cease and desist action against Ryanair, which if accepted will bring fines against the firm if the practices continue".
Yesterday, Aviation Regulation Commissioner Cathy Mannion said action will be taken against Ryanair if the company's handling of compensation claims over their recent flights cancellation is not deemed to be satisfactory.
Ryanair has defended its handling of the problems stemming from a pilot shortage that has led it to axe thousands of flights in Europe.
The wave of cancellations has now extended into early 2018.