On 28 June 2020, Chui stated on his Facebook page that he had been among those arrested during protests against the looming National Security Legislation.[3][4]
On 8 December 2020, Chui was arrested for his alleged involvement in the unauthorized 1 July march that year. Seven other democrats were arrested the same day on similar charges.[5]
On 6 January 2021, Chui was among 53 members of the pro-democratic camp who were arrested under the national security law, specifically its provision regarding alleged subversion. The group stood accused of the organisation of and participation in unofficial primary elections held by the camp in July 2020.[6] Chui was released on bail on 7 January.[7]