British authorities allege protesters who oppose a third runway at Heathrow Airport plan to pose as passengers to disrupt hundreds of flights.

At least 1,000 members of the protest group Climate Rush intend to block departure gates Monday night in Terminal 1, which handles 13,000 departing passengers daily, The Times of London reported Saturday.

Climate Rush is calling the protest a "peaceful picnic" while officials of BAA, the airport's owner, fear it could turn into a mob scene, The Times reported.

BAA has been negotiating with Climate Rush through the group's Web site on Facebook, the social networking site.

An estimated 700 homes near Heathrow would be demolished to make way for a third runway while noise in the area would increase dramatically from more flight traffic, said Climate Rush officials.

BAA has said it needs the third runway to handle increasing passenger traffic.