Survivors and families of victims of the bungled Manila hostage rescue three years ago will sue the Philippine government if their demands are not met by Friday.
The threat was made by Tse Chi-kin, the older brother of a tour guide killed in the bus hijacking drama in August 2010.
Friday marks the third anniversary of the incident in which eight Hongkongers - including Tse's brother, Masa Tse Ting-chunn - were killed after former policeman Rolando Mendoza took the 22 Hongkongers and three Filipinos on board the bus as hostages.
But this year, the day is also the legal deadline for survivors and victims' families to take action in the courts against the Philippine government.
The incident, including the gun fight that ensued when negotiations broke down after a 10-hour standoff, was broadcast live on television worldwide.
The Philippine government was roundly criticised over the police officers' handling of the situation and some held it responsible for the failure of the rescue attempt and the gun battle, which lasted 90 minutes.
Manila has never offered an apology for the incident.
"Our demands have stayed the same throughout the years, so we are giving [the Philippine government] one last week to meet them," said Tse.
"If not, we are prepared to take [it] to court."
Tse is demanding an apology from the Philippine government, an offer of compensation, punishment for the officials responsible for the bungled police operation and improved tourist safety.
Tse, 35, said that he was determined to pursue the demands so that he could move on emotionally. He said the aftermath of the incident had to be dealt with properly, or Hongkongers could never be sure whether their government would protect them if they ran into trouble abroad.
Tse said he had spent the past three years assiduously lobbying the government to take more action, but to no avail. He said monitoring the progress in the fight for his demands had become a daily habit and had worn him down.
The success of Taiwan's government in obtaining an apology from Manila for the fatal shooting of a Taiwanese fisherman by Coast Guard personnel also made Tse more determined to pursue his cause.
Li Yick-bin, a 74-year-old survivor of the hostage drama, said: "If you look at [the Taiwan incident], at least they were given an answer, an apology [by the Philippine government]. But us? It's like we are second-class people and can be ignored."
Li criticised the Hong Kong government as being helpless and Beijing for not backing Hongkongers.
"The Chinese government doesn't even treat Hongkongers as its own people," he said. "[Beijing] actually did nothing to help. At least the Taiwan government threatened to stop importing Filipino maids … you can see the difference some political pressure can make."
A spokesman for the Security Bureau said Hong Kong "will do its utmost to continue to follow up on the incident".
He said the local government had been liaising with Beijing and the Philippine consulate general to urge Manila to follow up on the four requests made by Tse and his group.
Since 2012, the Hong Kong government had contacted the consulate general 23 times for action on the requests, he said.
Secretary for Security Lai Tung-kwok said yesterday that the government would continue to pursue the matter.
The Ministry of Foreign Affairs repeated the requests of the victims and their families to the Philippines at a foreign affairs meeting in June, he said.