Hundreds of people risked arrest in London on Saturday under British terrorism laws during a protest of the government’s decision to ban a pro-Palestinian activist group.

The group, Palestine Action, was designated a terrorist organization in July after two of its members broke into a British military base and damaged planes to protest Britain’s military support for Israel. It was the first organization to be banned under a segment of Britain’s legal definition of terrorism that covers serious property damage, rather than violence against people, to advance a political cause.

The designation put Palestine Action on the same legal footing as groups like Al Qaeda, and it opened its supporters to a wide range of offenses that criminalize membership or involvement with the group, as well as public expressions of support.

Saturday’s arrests escalated the confrontation between the British authorities and supporters of Palestine Action over applying the terrorism law to protests, an otherwise protected form of expression in Britain.

As Big Ben struck 1 p.m., hundreds of protesters who had gathered outside Parliament took out pens and wrote “I oppose genocide. I support Palestine Action” on pieces of cardboard and paper, before sitting silently on the ground.