A judged has granted leave for a judicial review of a report by the Police Ombudsman into the attack on the Heights Bar in Loughinisland in 1994.
Families of the victims said they were surprised and disappointed retired officers continue to rub salt into their emotional wounds, with what they called a "vexatious challenge".
The report published last June said police informers were involved, adding that collusion was "a significant feature" of the murders.
The report was the result of a five-year investigation by the office of the Police Ombudsman.
Those taking the legal action argue that the Ombudsman acted beyond his legal powers and want his report quashed.
At a press conference launching the report, Ombudsman Dr Michael Maguire said he had "no hesitation" in saying there had been collusion.
But he said there was insufficient evidence to recommend criminal charges for any of the officers who colluded with the UVF gang, he added.
The findings were strongly criticised by unionist politicians and the Northern Ireland Retired Police Officers' Association.
Chief Constable George Hamilton also said he was surprised the Ombudsman did not arrest and charge officers he said had been involved.
A judge has granted permission for two retired police officers to challenge the report; one of them is Raymond White, a former RUC Assistant Chief Constable and senior Special Branch officer, who is now chairman of the Retired Police Officers' Association.
They have been granted leave to judicially review the report on a number of grounds.
These include an assertion that the Ombudsman acted "ultra vires" - beyond his powers - because there was no legal basis for the investigation and subsequent report.
The applicants claim the Ombudsman failed to establish any basis of belief that a serving or retired police officer had committed a criminal offence.
They are seeking a court order quashing the report.
They also want a declaration that the findings were "flawed and misconceived".
Niall Murphy, a solicitor for the Loughinisland families, said Dr Maguire's detailed and evidence-based report was unambiguous in his finding of collusion.
He said: "The victims and survivors are further distressed and disturbed that despite having written to the Retired Police Officers' Association and the court seeking formal notice party status, no party has sought to update the families, instead the victims and survivors have found this out via the media, which they consider to be nothing short of disgraceful."
In a statement to the BBC, Raymond White said: "We have every sympathy with the families connected to the Loughinisland tragedy. We are not challenging them, but the powers of the Police Ombudsman.
"The Ombudsman produces reports that do not contain any actual evidence about individuals and files are not sent to the director of public prosecutions recommending prosecution.
"But they conclude there was collusion, which infers criminal intent.
"If files were sent to the PPS to make a decision and retired officers were taken to court, they would have the opportunity to see the evidence and to challenge it.
"But that does not happen, instead they are indicted in the court of public opinion, with no right of appeal."
The Ombudsman has been given two months to respond to the case made by the retired officers.
The judicial review is expected to take place later this year.
A spokesman said the Police Ombudsman's office had acted totally within its powers and would strongly contest the legal challenge.
Retired police officers have won High Court permission to challenge a report which said there was collusion between RUC officers and loyalist gunmen who killed six Catholics 23 years ago.