Airlines will cut 20 percent of flights departing London's Heathrow Airport on Monday following a directive by the airport's owner amid a growing dispute over how to handle tougher security measures.

Airport operator BAA Plc said on Sunday carriers had to cut departures further this week to cope with congestion caused by tightened security or else it may ban them from using the airport.

The directive followed a 30 percent reduction in flights on Sunday as airlines struggle with tight security at British airports following what police said was a foiled plot to blow up transatlantic airliners.

British Airways said it was complying with the directive and expected to cut 20 percent of its flights from Heathrow on Monday. This included 39 short-haul flights out of 202 and five long-haul flights out of 76.

The airline said it expected to operate a full European and long-haul schedule from London Gatwick but some domestic flights would be affected.

Virgin Atlantic criticized the directive, saying it favored airlines like British Airways which could cut less-lucrative short flights and keep most of its long-haul operations running.

There is no level playing field, a Virgin spokesman said.

Virgin, which operates only long-haul flights, also called on BAA to let it operate some flights from London's other airports such as Gatwick. Virgin plans to cancel three flights on Monday.

The directive at Heathrow applies to airlines with four or more flights a day from the airport.

BAA threatened to deny airlines the use of airport facilities if they did not comply, according to a memo a source familiar with the situation said was sent by the airport's chief executive Tony Douglas to airlines over the weekend.

Any airline not complying with this Chief Executive Officer instruction by attempting to operate into or out of Heathrow will be considered to be in breach of the conditions of use for Heathrow airport and the use of airport facilities will be denied, the memo, emailed to Reuters, said.

A spokesman for British airline bmi said it was cutting four flights on Monday and was unaware of the directive.

A spokesman for BAA declined to comment on bmi's position. Bmi has more than 80 flights scheduled to depart from Heathrow on Monday, according to its Web site.

Ryanair, Europe's largest low-cost airline, earlier called on Britain to revise what it called heavy handed airport security measures and said London's airports were on the brink of collapse.

The Dublin-based group canceled 20 percent of flights out of its main London Stansted base over the weekend.

British Airways earlier called on BAA to increase resources with chief executive Willie Walsh complaining: BAA is unable to provide a robust security search process and baggage operation.

BAA's chief at Heathrow, Tony Douglas, said that if extra searches were maintained, long queues and cancellations were inevitable. They're not sustainable measures, he said.

I don't know how long it's likely to go on, he told BBC television.

British low-cost carrier easyJet said it expected to cancel about 30 flights on Monday.