Airlines don’t want to say it, so the International Air Transport Association will: Up to five million tickets may have to be canceled in the event of a hard Brexit.

The Times reports that London and Brussels agreed that in the event of a no-deal Brexit, the number of flights between the U.K. and the continent would be capped at last year’s levels. That would mean carriers could have to cancel thousands of flights, leading to higher ticket prices and many ruined vacations. IATA counted five million seats on the additional flights between the U.K. and Europe that might be affected, many of them scheduled for the peak summer holiday season.

“That current flight levels will be protected even with a hard Brexit is an important assurance. But with two months left until Britain leaves the E.U., airlines still do not know exactly what kind of Brexit they should be planning for,” Alexandre de Juniac, IATA’s director general and CEO, said in a statement. “And there is legal and commercial uncertainty over how the Commission’s plan to cap flight numbers will work.”

Prime Minister Theresa May is scrambling to convince the U.K. parliament to accept her Brexit deal before March 29. If it’s not approved, Brussels’ contingency plan will go into effect. In addition to the cap, Politico reports British airlines would lose the right to operate intra-EU flights.

The Times reports British Airways, Easyjet, Ryanair, and Jet2 have all expanded their European routes this year, but none have so far informed passengers about the potential implications of a hard Brexit. Only the Hungarian airline Wizz Air has warned British travelers of the no-deal rules, which also would require British travelers to have at least six months left on their passports in order to visit EU countries, though they wouldn’t need a visa. In the case of a hard Brexit, passengers would be refunded the costs of the canceled flights, but they’d be on their own to compete for new seats.

Ryanair COO Peter Bellew said this weekend he didn’t anticipate Brexit to cause an overnight stoppage, the Irish Times reports. Previously the airline’s CEO, Michael O’Leary, had warned of flights being grounded for weeks after a hard Brexit, but Bellew said Ryanair had set up subsidiaries specifically to avoid that problem.

Gate Gourmet, the Swiss-based worldwide leader in airline catering, has begun stockpiling meals, snacks, toilet paper and cutlery in its U.K. warehouses, Bloomberg reports. The company aims to have 10 days’ worth of stock to be able to bridge any Brexit-related disruption.

“In the small window remaining before Brexit, it is imperative that the EU and UK prioritize finding a solution that brings certainty to airlines planning growth to meet demand and to travelers planning business trips and family holidays,” de Juniac said.