Climate activists from Extinction Rebellion are considering using drones to shut Heathrow Airport this summer in a campaign against plans to build a third runway.

The proposal would mark a significant escalation by the group, which mobilised thousands of people in a peaceful civil disobedience campaign that brought parts of central London to a standstill in April.

“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,” Extinction Rebellion said in a statement released Thursday.

“This is not about targeting the public, but holding the government to their duty to take leadership on the climate and ecological emergency,” the group said.

The group said it understood “the action will cause disruption to a great number of holiday makers, 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.

“Holiday makers are being given advance notice to change travel plans.”

Security forces have been on alert since December, when Gatwick Airport outside London was forced to cancel flights over several days due to large drones near the perimeter. Extinction Rebellion was not involved in that incident, senior members of the movement said at the time.

In an internal proposal written by volunteers and seen by Reuters, activists suggested using drones to force authorities to ground flights at Heathrow Airport while other protesters held picnics. The activists said they would avoid any risk to aircraft by informing the authorities of their plans in advance.

If the government does not cede to their demands after disruption on June 18, the activists proposed shutting the airport for the first two weeks in July.

Extinction Rebellion’s commitment to non-violent civil disobedience to press for faster cuts in greenhouse gas emissions has spurred offshoots in more than a dozen countries and pushed climate change up the political agenda.

Nevertheless, the planned Heathrow action is likely to divide opinion within the movement. Some volunteers believe that governments will only treat the climate crisis with sufficient urgency if faced with large-scale disruption, including to transport networks.

Others fear that disrupting air travel may alienate large numbers of people who might otherwise have been sympathetic to the movement’s demands.

As a self-organising, highly decentralised movement, Extinction Rebellion volunteers have a lot of autonomy, making it hard to predict whether the drone proposal will win enough support to proceed.

Parliament backed a plan to build a third runway at Heathrow Airport last year, but the expansion faces opposition from local communities and environmentalists.

Heathrow Airport is owned by Ferrovial, Qatar Investment Authority and China Investment Corporation among others.