Hong Kong authorities arrested dozens of ex-lawmakers and pro-democracy campaigners in early morning raids on Wednesday.
It's the biggest crackdown yet against the opposition camp since the city's national security law was brought in last June, with more than 50 people taken into custody on suspicion of violating the law.
According to the Facebook page of the Democratic Party, Wednesday's sweeping arrests included former lawmakers and activists James To, Lam Cheuk-ting and Lester Shum.
The Democratic Party said police arrested the activists for participating in an independently organised, unofficial primary in July to select candidates for last September's legislative election.
In the end that vote was postponed for a year due to public health restrictions.
The pro-democracy movement had hoped to win a majority - and some candidates wished to use it to block government proposals, which the Democratic Party says was seen as an "act of subversion, in violation of the national security law."
Local media said the police operation included searches of the offices of the Hong Kong Public Opinion Research Institute and lawyers who helped organise the primaries.
The Hong Kong government and Beijing warned that the unoffical primaries could violate the national security law.
Under the law, anything Beijing broadly defines as secession, subversion, terrorism and collusion with foreign forces is punishable by up to life in prison.
The latest arrests have drawn widespread criticism from rights groups and activists, who accuse Beijing of further undermining democratic freedoms in the former British colony.