LONDON — The British government confirmed Monday that it will designate campaign group Palestine Action a terrorist organization after its activists breached a military base and damaged two planes.

Home Secretary Yvette Cooper said the pro-Palestinian organization would be proscribed under an order placed before parliament on June 30.

The decision — which has sparked some debate over civil liberties in the U.K. and a pushback protest from Palestine Action — came after the group gained access to Royal Air Force (RAF) Brize Norton in Oxfordshire last week and sprayed red paint into the engines of two Airbus Voyager aircraft.

Brize Norton is the largest RAF station and contains the outfit’s Air Mobility Force and Air to Air Refueling forces. The home secretary said the “disgraceful attack” led to her decision and that the damage was “unacceptable.”

Cooper’s written statement said Palestine Action had planned a “nationwide campaign of direct criminal action against businesses and institutions” including national infrastructure and defense allies that support NATO and Ukraine.

The proscription under the Terrorism Act 2000 makes it a criminal offense to belong to the group, invite support for the organization, express opinions in favor or organize a meeting for the group. Penalties would be 14 years in prison or a fine.

Wearing clothing backing Palestine Action could lead to six months in prison alongside a fine up to £5,000.

‘Extremist criminal group’

Hundreds of people attended a Palestine Action demonstration in Trafalgar Square to oppose the home secretary’s actions.

Chants of “we are all Palestine Action” and “we won’t be silenced” tried to show the now proscribed organization wasn’t a fringe group and had large support.

“Seeing thousands of men, women and children being slaughtered by the Israeli regime shocked people into coming and protesting and making their voice heard,” said 54-year-old attendee Paul Nelson.

He condemned the government proscribing a “peaceful, non-violent campaign” and called damaging property “a valid form of democratic right and free speech.”

Nelson added: “You are fundamentally attacking our democracy.”

Britain’s most senior police officer, Metropolitan Police Commissioner Mark Rowley, said he was “shocked and frustrated” at the decision to hold a demo in support of “an organised extremist criminal group.”

“The right to protest is essential and we will always defend it, but actions in support of such a group go beyond what most would see as legitimate protest,” Rowley said in a statement.

But Labour peer and former director of civil liberties organization Liberty Shami Chakrabarti said the government might be going too far and argued most people wouldn’t see the group as a terrorist organization.

“To proscribe Palestine Action on the information that we have all seen … would be a new departure,” Chakrabarti told the BBC Monday.

While arguing people might be prosecuted or imprisoned for specific offenses, the Labour peer said it was “another thing altogether to proscribe a whole group, and that means anybody fairly vaguely associated with it, to ban them [as] terrorists.”