The pro-democracy group behind Hong Kong's annual Tiananmen Square vigils set up a showdown with authorities on Tuesday as they defied a police deadline to cooperate with a "national security" investigation into their activities.
The Hong Kong Alliance organised three decades of vigils commemorating the victims of Beijing's Tiananmen Square crackdown in 1989.
It is now being investigated under a powerful national security law that China imposed on Hong Kong to stamp out dissent after huge and often violent democracy protests broke out two years ago.
Last month police ordered the group to hand over financial and operational details, accusing it of working as a "foreign agent".
The request included the personal details of all members since its founding in 1989, all meeting minutes, financial records and any exchanges with other NGOs advocating democracy and human rights in China.
On Tuesday, the deadline for the request, members of the alliance handed a letter explaining their refusal to cooperate.
"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," Chow Hang-tung, a barrister and alliance member, told AFP on her way to the police station.
Tsui Hon-kwong, one of the alliance's directors, also filed a judicial review in the courts arguing that the police request for information was illegal.
"The Commissioner... provides no explanation on why he reasonably believes that the Alliance is a foreign agent, thus hampering the Alliance from making any concrete rebuttal or clarification," Tsui argued in his application.
"This offends the rules of natural justice."
Hong Kong authorities had previously warned that alliance leaders faced jail or fines if they refused to cooperate with their probe.
"To avoid bearing the legal risk, the organisation concerned should immediately turn back before it is too late," the Security Bureau said on Monday.
China is currently remoulding Hong Kong in its own authoritarian image.
Dozens of democracy figures have been arrested and an official campaign has been launched to purge the city of anyone deemed "unpatriotic".
The alliance, officially titled the Hong Kong Alliance in Support of Patriotic Democratic Movements of China, was once one of the most visible symbols of the city's political plurality.
Each June 4 it organised large candlelight vigils in Hong Kong's Victoria Park that were routinely attended by tens of thousands of residents, the crowds swelling in recent years as anger over how Beijing was running the city intensified.
Slogans at the vigils often called for democracy in China and an end to one-party rule.
Tolerance for such political defiance has since ended.
The last two Tiananmen vigils were banned by the police and earlier this year city officials shuttered a museum operated by the alliance.
Authorities in China and Hong Kong have also said that future vigils would likely break the new security law.