The government is considering plans for a new third runway at Heathrow
People against Heathrow airport's expansion have met to discuss what to do if it gets the go-ahead to build a third runway and sixth terminal.
About 100 residents, trade unionists and MPs will met at a conference in Harlington, west London, on Saturday.
They were be joined by green protesters from the Camp for Climate Action.
Topics discussed included the possibility of "mass direct action" if expansion plans are approved by the government.
On Sunday, the Camp for Climate Action protesters will set off on a "climate caravan" from the village of Sipson, near Heathrow, to Kingsnorth in the Medway area of Kent, where this year's climate camp is being held.
This year's protest, which is being held from August 4 to 11, will take place at the site of Kingsnorth power station, owned by the E.On company.
Protesters have said they want to force the existing power station to shut but E.On has been granted a court injunction to protect the site.
Greenpeace chief executive John Sauven said: "Aviation is the UK's fastest-growing contributor to climate change. The plans to expand Heathrow must be stopped.
"At a time of runaway climate change and rocketing oil prices they make no sense at all."
John Stewart, of the Heathrow Association for the Control of Aircraft Noise (Hacan) said protests plans could range from "mass letter-writing to mass direct action".
"The significant thing is that we have had MPs sharing the same platform as local campaigners, Greenpeace and Plane Stupid," he said.
"It shows that there is unity among a whole diverse range of people on this matter and the possibility for a whole diverse range of tactics.
"What unites us is an utter determination to win this battle."
But business groups and airlines have claimed the third runway is essential.
Lord Soley, campaign director of pro-expansion group Future Heathrow, said opinion polls showed local people were in favour of expansion.
"Local people know that the airport is vital to the local economy and supports jobs and business," he said.
"A third runway will only go ahead within environmental limits on noise and air quality."