Pledge comes as secretary for civil service says government employees taking part would violate code of conduct.
The three volunteers were detained in Causeway Bay, where crowds had gathered to mark protest anniversary on Friday night.

Hong Kong activists organising an unofficial referendum on whether to carry out class boycotts in tandem with general strikes over the national security law vowed to press ahead, despite the arrest of three volunteers.
The pledge came as the secretary for civil service warned government employees that taking part would be a violation of their code of conduct.

The vote, originally planned for this Sunday 14 but postponed until June 20 over the prospect of bad weather, is being co-organised by
– the Hong Kong Secondary School Action Platform,
– the Demosisto political party of activist Joshua Wong Chi-fung
– and more than 20 labour unions linked to the anti-government movement.

The State Council’s Hong Kong and Macau Affairs Office (HKMAO) on Friday 12 accused Wong and others of exploiting secondary school pupils.
The boycotts and strikes are intended to fire a warning shot to Beijing as it prepares to draft the legislation, which aims to prevent, stop and punish secession, subversion of state power, terrorism and foreign interference in the city.

Isaac Cheng Ka-long, spokesman for the Hong Kong Secondary School Action Platform, on Saturday said organisers would not be deterred.
“I think everyone will be a target when we are holding this referendum, but we won’t be afraid and we will hold together,” said Cheng, also a vice-chairman of Demosisto. “We urge secondary students and adults to act and join the referendum [next] Saturday 20.”
Cheng said three volunteers of the platform were arrested on Friday 13 night in Causeway Bay, where crowds had gathered to mark the anniversary of the first major clashes in the city that launched last year’s social unrest.
The three were setting up booths to promote the referendum when police rushed in and arrested them, Cheng said, adding one female volunteer, a Form Five student, was hurt in the operation. A video of the arrest appeared to show a police officer kneeling on her neck, he said.
“It is obvious that the police action was to cooperate with the threatening statements from the HKMAO and the liaison office … as to stop us from promoting the referendum and further strike actions,” the platform said. “We believe this vote is now beyond taking part a strike or not, but a key gesture to safeguard our [freedoms in] campus.”

Secretary for Civil Service Patrick Nip Tak-kuen doubled down on his warning, a day after the government issued a statement condemning a civil service union that planned to take part in the referendum.
He said those urging colleagues to strike would breach the civil service code and the bureau would “follow up” with them on the matter. “Civil servants have a responsibility to support and implement the national security law,” Nip said on a radio programme on Saturday 13.
“Some have claimed they are only gathering opinion and concerns about the law. But it is a referendum initiated by various unions … the real purpose is very obvious.”

The Union for New Civil Servants, which emerged from last year’s anti-government protests, earlier rejected the criticism, saying it deeply regretted the government’s disregard for its efforts to gauge colleagues’ views on the legislation. It also said the union had no preconceived standpoint on the matter.
On Saturday, union chairman Michael Ngan Mo-chau said they would meet the press and respond on Monday 15.

Secretary for Civil Service Patrick Nip Tak-kuen also said the government had been studying its policy requiring employees to swear allegiance to the administration and would report the findings to the Legislative Council next month.
He said various employees’ unions would be consulted, while reiterating the needs to strengthen national identity among civil servants. He earlier raised eyebrows by calling on all civil servants to understand that they served both the city and the country.
Speaking after the radio show, he again reminded government employees they had to be careful when expressing their views on social media, even though freedom of expression had been guaranteed in the Basic Law.
“If you are at the same time holding a chair as a civil servant, you have to be mindful about your public expressions and your acts, to comply with the requirements and your responsibilities as a public office holder,” he said.