London’s Heathrow Airport and three major airlines lost the bulk of their appeal against an order by the nation’s aviation regulator to cut airline charges by around 20% per passenger next year.

The Competition and Markets Authority, Britain’s antitrust watchdog, said on Tuesday that Civil Aviation Authority’s decision to lower charges for airlines using the airport was “not wrong on most of the issues,” according to its statement. However, it ordered the CAA to reconsider three parts of its pricing decision without specifying what they were.

“The CAA’s Heathrow price control struck broadly the right balance between ensuring prices for passengers are not too high and encouraging investors to maintain and improve the airport over time,” CMA executive Kirstin Baker said in the statement. However, she added “there are a handful of smaller issues we have ordered the CAA to look at again and it has agreed to do this swiftly.”

Heathrow and the world’s biggest airlines have clashed over the charges, which are among the highest globally. The CAA said in March the levy should drop to £25.43 ($30.98) per passenger in 2024 from £31.57.

British Airways Plc, Delta Air Lines Inc., and Virgin Atlantic Airways Ltd. had also appealed the ruling.