Climate campaigner Greta Thunberg pleaded not guilty to a public order offense in London after being arrested while blockading an oil and gas conference.

The Swedish activist, 20-years-old, was at Westminster Magistrates Court to plead with nine other protesters. A trial is set for Feb. 1.

Thunberg was arrested on Oct. 17 during a protest at Energy Intelligence Forum at the Intercontinental Hotel where oil and gas executives were speaking. The activist have championed the voice of young people in the global fight against climate change since her strike against attending school captured international attention in 2018.

Outside Westminster Magistrate’s Court on Wednesday morning, about 20 protesters held placards with slogans including “Fossil Free London” and “Oil Money Out” chanting in support of urgent action on climate change.

Supporters in the public gallery were chastised by the judge after they laughed when the prosecution lawyer described the conference as seeking to discuss sustainable energy solutions.