Hong Kong national security police on Thursday arrested a veteran labor activist who is also the wife of an organizer of annual vigils commemorating China’s 1989 crackdown on pro-democracy protesters, two people close to her said.

Officers arrested Elizabeth Tang, the wife of Lee Cheuk-yan, outside Stanley Prison but it was still unclear for what reason, said the people, who declined to be identified for fear of government retribution.

The move was seen as part of a crackdown on the city's pro-democracy camp following massive anti-government protests in 2019. Many activists have been jailed or silenced under a sweeping National Security Law imposed by Beijing.

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Tang is currently the general secretary of the International Domestic Workers Federation.

She was a former leader of the now-defunct Hong Kong Confederation of Trade Unions, the city's largest pro-democracy trade organization. Before the group's disbandment, it had been on a list of activist groups targeted by pro-Beijing media in the name of national security. Her husband Lee was also a leader.

Lee was also a leader of the Hong Kong Alliance in Support of Patriotic Democratic Movements of China, which voted to disband in 2021 following the imposition of the security law.

The alliance was best known for organizing large candlelight vigils in Hong Kong on the anniversary of the Chinese military’s crushing of the 1989 Tiananmen Square pro-democracy protests. Supporters say its closure shows that freedoms promised to Hong Kong when it returned to Chinese rule in 1997 are eroding.

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Lee and two other former alliance leaders, Chow Hang-tung and Albert Ho, were arrested and charged with inciting the subversion of state power under the security law in 2021. The alliance itself was charged with subversion. Lee is now in custody.

The South China Morning Post quoted an unidentified source familiar with the case as saying she was arrested on suspicion of colluding with foreign forces after visiting her husband in prison.

The National Security Law criminalizes secession, subversion, terrorism and collusion with foreign forces to intervene in the city’s affairs.

Pro-democracy newspaper publisher Jimmy Lai is also facing collusion charges under the law.