“The information [sought] includes the member list, the group’s financial reports and activities information,” a senior police source said.

Another police source said national security officers were specifically looking for links between the alliance and several different foreign organisations, including some based in the United States.

“We are investigating the relationship between the group and these foreign organisations,” the source said. “We are also looking into whether the group is the Hong Kong agent of overseas organisations and if it received any financial support or donations from those organisations.”

A police spokesman confirmed the force had evoked its power under the national security law but declined to provide further details.

Chow Hang-tung, vice-chairwoman of the alliance, confirmed that all seven members of its standing committee had received letters from the National Security Department, which had given them two weeks to respond.

She said they were still seeking legal advice on whether to hand over the relevant documents.

“But the allegation that the alliance is a foreign agent is ridiculous,” Chow said.

The letters informed recipients that police had reason to believe the group was a “foreign agent”, and demanded it hand over personal details of its leaders and full-time staff, along with other information dating back to 2014.

The information sought included details and financial dealings connected to the alliance’s activities with the New School for Democracy, Asia Democracy Network, China Human Rights Lawyers Concern Group, and other organisations funded by the US-based National Endowment for Democracy (NED).

Group behind annual June 4 Tiananmen vigil in Hong Kong decides to disband

Police also asked the alliance to explain its dealings with Mark Simon, the right-hand man of jailed media tycoon Jimmy Lai Chee-ying.

Among those who received the letters were alliance chairman Lee Cheuk-yan, and former Democratic Party leader Albert Ho Chun-yan, both of whom are in jail serving sentences for their roles in unauthorised protests. Ho is a founding member of the China lawyers concern group.

The 32-year-old alliance is the latest among a range of opposition and activist groups being targeted by the authorities in recent months, the crackdown stemming from their roles in the anti-government protests and social unrest of 2019.

Earlier this month, the Civil Human Rights Front, the umbrella group behind many of the city’s largest rallies over the past two decades, disbanded after police began investigating its legal status.

Days before that, the Professional Teachers’ Union, the city’s biggest union for teachers and a member of the front, announced its dissolution after being labelled as a “malignant tumour” by Beijing through state media and ostracised by the government.

The alliance has been unable to organise its flagship June 4 vigil for the past two years with police denying permission on public health grounds amid the coronavirus pandemic. Some of its leaders who still showed up at the traditional venue in Victoria Park last year were charged with organising or taking part in unauthorised assemblies.

The fate of the alliance, whose rallying slogans include calls to “end one-party dictatorship” in mainland China, has been uncertain since the imposition of the national security law in June last year.

Last month, the group reduced its standing committee membership to seven from 14, and dismissed all its staff members, citing a rapid deterioration of freedom in the city’s political landscape.

The police commissioner, with the secretary for security’s approval, has the power to demand information from any group with ties to Taiwan or foreign governments if it believes there is a need for the investigation and prevention of a national security offence.

The information required can include personal details of staff and members, the group’s activities, and its financial status.

The obligation applies to “every office bearer” and failure to comply constitutes an offence punishable by a fine of up to HK$100,000 (US$12,840) and six months’ imprisonment.

It is also an offence if the information provided is “false, incorrect, or incomplete”, which carries a fine of HK$100,000 and a jail term of up to two years.

“Police can exercise the power without an offence endangering national security being committed, as the rules can be applied for the purpose of investigation and prevention,” a barrister explained, asking to remain anonymous.

Organiser behind many of Hong Kong’s biggest protests to disband

The pro-Beijing Ta Kung Pao newspaper has alleged that Albert Ho, a key member of the alliance, was a former director of the New School for Democracy in Taiwan, and that the school had received funding from the NED.

The newspaper also accused the Confederation of Trade Unions, a group led by core alliance member Lee Cheuk-yan, of receiving money from the NED’s American Centre for International Labour Solidarity.

In May 2019, the alliance and the New School for Democracy co-organised a series of seminars in Taipei to mark the 30th anniversary of the Tiananmen Square crackdown.

At a special meeting of the alliance’s standing committee on Monday, it was decided that the embattled group would be dissolved.

The alliance will be formally disbanded if an emergency general meeting of member groups endorses that decision.

Additional reporting by Lilian Cheng