Three ex-Hong Kong lawmakers were arrested in connection with a disruptive protest in the legislative chamber, as the Beijing-backed government ramps up pressure on the city’s beleaguered opposition.

Eddie Chu, Raymond Chan and Ted Hui were arrested by police Wednesday morning, the former lawmakers wrote on their Facebook pages. The Hong Kong police confirmed it arrested three suspects matching the ages of the ex-lawmakers, citing allegations stemming from an attempt to disrupt a June vote in the Legislative Council on a measure banning criticism of the national anthem. The statement didn’t name the individuals.

The three were accused of contempt and attempt to cause harm with a dangerous substance in connection with foul-smelling substances thrown onto the legislative rostrum during the proceedings, police said. Chu, Chan and Hui didn’t immediately respond to requests for comment.