London Gatwick airport and discount carrier Wizz Air Holdings Plc joined forces to demand that Britain force airlines to surrender more unused operating slots next summer.

The pair have written to U.K. Transport Secretary Grant Shapps urging him to back a return to an 80% use-them-or-lose-them threshold in a consultation document expected in coming days.

Regulations for the current winter schedule, introduced to shield airlines whose services have been hit by the coronavirus crisis, allows incumbents to temporarily return any operating slots they don’t need and pick them up the following year, and to use only 50% of those that remain.

Gatwick says the rule has left its runway underused, with IAG SA’s British Airways mothballing short-haul routes, Virgin Atlantic Airways Ltd. halting long-haul flights and Norwegian Air Shuttle ASA retaining slots from a defunct North Atlantic arm. Wizz wants to establish a major hub at Gatwick to compete with EasyJet Plc there, but says it won’t do so only to be stripped of slots later. Edinburgh and Belfast International airports also signed the letter, according to a statement Tuesday.

“The continued use of the waiver would result in most airlines continuing to under-deliver on capacity, whilst deliberately hoarding slots to protect their market position,” the letter says. “This would significantly harm competition by acting as an intentional barrier preventing other carriers, including new market entrants, from flying these slots instead.”

The companies said they understand that the European Union is considering a return to the 80:20 rule next summer. The bloc’s winter stipulation requires the use of 50% of takeoff and landing positions from October through March like the U.K., but without the option to temporarily hand in slots beforehand.

Gatwick, owned by French builder Vinci SA, says it’s operating only 58% of pre-pandemic routes, compared with 82% at London Heathrow, Britain’s leading hub, and 85% at discount base Stansted. Yet the airport has had requests for a record 262,000 slots next summer, 40,000 more than in 2019.

IAG SA Chief Executive Officer Luis Gallego said Monday that British Airways is set to launch a new unit offering European from Gatwick in March following a deal with cabin crew and an earlier accord with pilots, without disclosing how big the operation might.

Virgin Atlantic “will probably move a bit into Gatwick” once its Heathrow capacity has reached 2019 levels, most likely after April next year, CEO Shai Weiss said.

The Department for Transport had no immediate comment.