The Civil Human Rights Front will not provide records of all the protests it has organized over the past 15 years to the police, convener Figo Chan Ho-wun said.
This came after the police's societies officer demanded the group provide information about their income and expenditure, as well as rallies they organized, over a suspected breach of the Societies Ordinance.
In his reply, Chan criticized the police probe into the front - which was established in 2002 - and their questioning of whether it is an illegal society.
"The front has adhered to its principles to be lawful, peaceful, rational and nonviolent since its establishment, and it has been meeting with the police to hold rallies and marches multiple times a year to allow Hongkongers to voice their concerns," Chan said.
"If the front is an illegal society, why did the police and government departments collaborate with us?"
Chan added that government departments, including the police, have never demanded the front register itself or warned that it was an illegal society.
Police representatives have previously also praised the front as "a big brand" that has been "cooperating very well with the police," according to Chan, who added this can be proven by a chief inspector's testimony in court recently.
He also said as Hongkongers have freedom of association according to the Basic Law, and that he does not agree that the front is an illegal society. Therefore, he will not provide the information requested by the police officer overseeing societies' affairs.
Asked whether he was worried authorities would see the front as "uncooperative" for not responding to the questions, Chan said it is already a breach of the law to submit incomplete information or not respond to questions.
"But I have to say it is very hard for us to submit a complete reply. Which society will keep its information for 15 years? Not to mention that I was only a primary student 15 years ago," Chan said.
According to the Societies Ordinance, a person providing false, inaccurate or incomplete information to the societies officer is liable to an HK$20,000 fine.
Meanwhile, the Civic Party distanced itself from the Hong Kong Alliance in Support of Patriotic Democratic Movements of China, as chairman Alan Leong Kah-kit said the party never joined the alliance.
Leong said his party has never joined the alliance and therefore cannot "quit."
This came after pro-Beijing heavyweights said the five major principles of the alliance - including "ending one-party rule" - might breach the national security law, which prompted three councillors' offices to part ways with the alliance, according to the alliance's secretary Richard Tsoi Yiu-cheung.
Tsoi said the alliance currently still has over 200 organization members and therefore the departures have not had a significant impact.
He added that the alliance will keep organizing the annual June 4 vigil according to its original plan, while sticking to its principles and slogans.