Extinction Rebellion activists are threatening to shut down Heathrow Airport with drones.
The climate change protest group vowed to stage a one-day demonstration in June and then 10 further days in July – unless the government cancels plans for expanding the airport.
Ten days of protests across central London in April saw 1,130 people arrested for various offences.
Heathrow Airport said the plan was “reckless” and could “endanger lives”.
Extinction Rebellion said it was in talks with its members about taking carrying out “nonviolent direct action to ensure Heathrow authorities close the airport” on 18 June.
It said it would “act to shut the airport down for up to 10 days from 1 July” if the government does not cancel all Heathrow expansion.
The plan to use drones was revealed in a leaked consultation document shared between group members.
A Heathrow spokesman said: “This is reckless action that if carried out could endanger the lives of the travelling public and our colleagues.
“We agree with the need to act on climate change, but that requires us to work together constructively – not commit serious criminal offences just as hard-working people prepare to spend a well-earned holiday with their family and friends.”
Last month in central London the group’s tactics included asking volunteers to deliberately get arrested to cause maximum disruption at roadblocks on Waterloo Bridge, Oxford Circus and Marble Arch.
Demonstrators also protested at Heathrow but did not cause disruption to flights.
A small group of mostly teenage activists briefly unfurled a banner near a tunnel which leads to Terminals 2 and 3 as several police officers watched on.
It was announced in January that police would be given new powers to tackle the illegal use of drones, after hundreds of flights at Gatwick Airport were disrupted by drone sightings in December.
Last year the government made it illegal to fly a drone above 400ft (120m) or within 1km (0.62 miles) of an airport.
The exclusion zone will now be extended to the current Air Traffic Zone around airports, which is approximately a 5km (3.1 miles) radius, with additional extensions from runway ends.
Endangering the safety of an aircraft is a criminal offence which can carry a prison sentence of up to five years.