Extinction Rebellion has threatened to shut down Heathrow Airport if the government does not cancel the planned expansion.
The environmental group has said they will use drones to shut down the airport for 10 days and demonstrations will start on 1 July.
The group said holidaymakers were being given advance notice to “change travel plans.”
A statement on their website published on Friday said, “Extinction Rebellion demands the Government begins to act on its declaration of a Climate and Environment Emergency by cancelling all Heathrow expansion.
“On June 18, we plan to carry out nonviolent direct action to ensure Heathrow Authorities close the airport for the day, to create a ‘pause’ in recognition of the genocidal impact of high carbon activities, such as flying, upon the natural world.
“If the Government does not cancel all Heathrow expansion, Extinction Rebellion will act to shut the airport down for up to 10 days from July 1.
“Extinction Rebellion is in the consultancy stage with its members on the proposed action.”
The statement added, “This is not about targeting the public, but holding the Government to their duty to take leadership on the climate and ecological emergency.
“The addition of the planned third runway would make Heathrow the single biggest carbon emitter in the UK – to expand the airport at this critical point in history would be madness.
“We understand the action will cause disruption to a great number of holidaymakers, however we believe that it is necessary given the prospect of far greater disruption caused by ecological and societal collapse, if we don’t act now.”