Ryanair has been given a deadline of 5pm to arrange compensation for hundreds of thousands of travellers affected by a wave of flight cancellations across the summer.
The Civil Aviation Authority (CAA) has told the airliner it must instruct passengers on how they will be re-routed onto other airlines and explain how it will work.
Ryanair must also state publicly it will offer reimbursement for all of those affected.
The CAA was “furious” after the budget airline cancelled a further 18,000 flights, a decision predicted to affect 400,000 customers.
It accused Ryanair of not complying with laws in how it handled the situation.
A spokesman from the company has said it will comply “fully” with whatever the CAA’s requirements will be.