The UK’s Civil Aviation Authority has taken enforcement action against Wizz Air Holdings Plc after many passengers complained about the carrier failing to reimburse them for delayed or canceled flights.

The Hungarian-based airline has committed to making policy changes to ensure it is compliant with passenger rights obligations, the CAA said in a statement on Thursday. Customers whose claims were incorrectly rejected by Wizz will get their money back, the regulator added.

Wizz was among airlines to suffer from disruption last summer when the industry was experiencing a surge in travel demand on top of staffing shortages following the Covid-19 pandemic. Many carriers struggled to cope with the imbalance and as a results, flights were disrupted and thousands of passengers were delayed or left stranded.

The CAA said there were major concerns about Wizz because of the high number of complaints made about the airline not refunding passengers for disrupted flights. The regulator will monitor Wizz’s compliance over the next few months and review some of the claims made to ensure passengers receive the money they’re owed.

“We made it clear to Wizz Air last year that the way it was treating passengers was unacceptable,” Paul Smith, joint-interim chief executive at the CAA, said in the statement.

Wizz has invested more than £90 million ($117 million) in improving operations to reduce flight cancellations, the airline said in a statement. Increased staffing, additional aircraft capacity and four new customer service centers are among the initiatives that Wizz has implemented to mitigate travel disruption, it said.