Labour says the jury in the Bain trial should never have been allowed near Mr Bain or his supporters after his acquittal in the High Court in Christchurch.
Mr Bain was seen hugging one juror as he left the court on Friday. Two jury members were later spotted at an after-trial party for supporters.
Opposition justice spokesperson Lianne Dalziel says the jurors should have been held together for a debrief and kept well away from the trial participants.
She says there needs to be a review of the way jurors are briefed and how well prepared they are for major trials.
Canterbury University associate law professor Ursula Cheer says such a review could provide support to ensure jurors' concerns are addressed.
The Law Society says there would have been public outrage if the jurors had attended a police celebration if the verdict had gone the other way.
Meanwhile, there is a possibility of fresh legal manoeuvring over the case.
Dunedin Coroner David Crerar is considering holding an inquest into the killings.
Chief Coroner Judge Neil Maclean and legal experts say a coroner's methods are different and an inquest could easily produce a different result from the High Court trial.
The head of Mr Bain's defence team, Michael Reed QC, concedes an inquest might be necessary for Robin Bain - but not for the others.
He says such an inquiry would be unmanageable.
Earlier, he said it would be tragic if Mr Bain had to endure a fresh legal ordeal.
Even if a coroner delivers a contrary verdict to the High Court, all legal experts say no further action could be taken against Mr Bain under the double jeopardy rule.
Mr Bain, 37, was found not guilty on Friday of the murders of five of his family members: his father Robin, mother Margaret, brother Stephen and sisters Arawa and Laniet in their Dunedin home on 20 June 1994.
The retrial lasted 13 weeks and heard evidence from 184 witnesses.
Mr Bain's original convictions were quashed by the Privy Council in 2007. He has spent 13 years in prison.