LONDON (AP) — Climate activist Greta Thunberg went on trial Thursday for refusing to leave a protest that blocked the entrance to a major oil and gas industry conference in London last year.

Thunberg, 21, was among more than two dozen protesters arrested on Oct. 17 after preventing access to a hotel during the Energy Intelligence Forum, attended by some of the industry’s top executives.

The Swedish environmental activist and four other protesters face a two-day trial in Westminster Magistrates’ Court on a charge of breaching a section of the Public Order Act that allows police to impose limits on public assemblies. She and four Fossil Free London protesters have pleaded not guilty.

Thunberg and other climate protesters have accused fossil fuel companies of deliberately slowing the global energy transition to renewables in order to make more profit. They also oppose the U.K. government’s recent approval of drilling for oil in the North Sea, off the coast of Scotland.

Thunberg sat in court in a black T-shirt and black pants, taking notes as a police officer testified about efforts to disperse demonstrators who had blocked several exits and entrances for hours outside the luxury InterContinental Hotel in central London.

“It seemed like a very deliberate attempt ... to prevent access to the hotel for most delegates and the guests,” Superintendent Matthew Cox said. “People were really restricted from having access to the hotel.”

Cox said protesters were lighting colorful flares and drummers were creating a deafening din outside the hotel as some demonstrators sat down on the ground. When officers began making arrests, other protesters quickly took their place, leading to a “perpetual cycle” that found police running out of officers to make arrests.

The protest had gone on for about five hours when Thunberg, outside the front entrance, was warned that she was going to be arrested. She was arrested after saying she planned to stay where she was.

Thunberg inspired a global youth movement demanding stronger efforts to fight climate change after staging weekly protests outside the Swedish Parliament starting in 2018.

Last summer, she was fined by a Swedish court for disobeying police and blocking traffic during an environmental protest at an oil facility. She had already been fined for the same offense previously in Sweden.