The Hong Kong Alliance in Support of Patriotic Democratic Movements of China said four members, including advocate and politician Chow Hang Tung, were arrested during the early hours of Wednesday.
The arrests were reportedly made under the country's controversial national security law that was implemented in 2020. Under the law, crimes of secession, subversion, terrorism and collusion with foreign forces are punishable by a maximum sentence of life imprisonment.
The alliance is known for organising candlelight vigils for the victims of China’s bloody crackdown on students in Beijing’s Tiananmen Square in 1989. The event was attended by massive crowds, but vigils have been banned for the past two years amid the Covid-19 pandemic.
The Hong Kong police had earlier asked the alliance to submit information, including financial records and personal details of all members since the group's formation. However, the organisation on Tuesday delivered a letter to the police rejecting the request. They were warned that failure to comply with the orders would result in a fine of $12,900 and up to six months in jail.
On Wednesday morning, police officers arrested the members from hotels and their offices. "We are going to respond, to say that we feel you have no legal grounds for your demands, so we are just going to ignore you," Ms Tung, the vice-chairperson of the alliance told AFP.
“The alliance strongly denies that we are any foreign agents," Ms Tung had earlier said at a press conference last Sunday. Her arrest comes hours before she was scheduled to represent detained opposition leader Gwyneth Ho, who was charged with conspiracy to commit subversion.
The investigation is part of China's ruling Communist Party's clampdown on Hong Kong's civil society after the mass protests seeking democracy in 2019.
In August this year, the Hong Kong Civil Human Rights Front, a prominent group behind the protests, chose to disband over the new security law. Since the enactment of the law on 30 June 2020, over 100 activists have been arrested, while others have gone into exile.
Two other alliance leaders Albert Ho and Lee Cheuk-yan are already in prison for their role in the anti-government protests.
"It’s absurd that, without providing any evidence nor court approval, the police can arbitrarily label an organisation as being a 'foreign agent'. Even before a trial begins, Hong Kong Alliance is presumed guilty. It completely violates the presumption of innocence in the past," said pro-democracy activist and politician Nathan Law.
"More importantly, this can happen to any local or foreign individual or organisation in the city. Individuals may be falsely accused of being a "foreign agent" and detained without a legal basis or court approval," he added.
Additional reporting from agencies