Three special interest groups have been granted permission to present evidence in court in the upcoming case of terminally ill 42-year-old lawyer Lecretia Seales.
In late March Ms Seales filed papers seeking a ruling to determine whether her GP could lawfully administer a lethal dose of drugs.
Today's decision comes on the same day she was told by her oncologist that chemotherapy would not be continued and had not been successful.
Her survival expectations have been revised and she will likely enter a phase of symptom management and palliative care.
Justice David Collins has this afternoon released his decision to allow the Human Rights Commission, the Voluntary Euthanasia Society of New Zealand and the Care Alliance to intervene in the case on a limited basis.
"In order to ensure Ms Seales is not unnecessarily burdened by the participation of the interveners, I am placing stringent conditions on the interveners' participation in this proceeding," he said.
The decision follows at hearing in the High Court at Wellington on Monday where the three groups sought to have their say on whether Ms Seales could end her life.
Voluntary Euthanasia supports Ms Seales' position, while the Care Alliance is opposed to assisted suicide and euthanasia. The Human Rights Commission takes neutral stance on the issue.
Ms Seales' lawyer, Dr Andrew Butler, opposed applications from the trio to join the legal challenge saying next month's trial did not need mountains of evidence from other parties.
He said it was strange to argue the other parties needed to help the Crown, because the Crown was already "the expert" in criminal law and Bill of Rights issues.
Care Alliance, a coalition opposed to euthanasia and assisted suicide, said groups that worked with the elderly, infirm and in the field of suicide prevention had to be heard as allowing Ms Seales' euthanasia would affect "the whole of society".
The Voluntary Euthanasia Society's said the issue was one of public policy and would "affect the rights and obligations of many in the future".
Human Rights Commission lawyer Matthew Palmer, QC, said the commission could play a helpful role as a neutral, independent party assisting the court. Dr Palmer also said the outcome of Ms Seales' bid would not be "confined" but would have effects on other people.
"If ever there was a case of widespread public importance, this is it."
He said the commission did not take a view on the morality of euthanasia but had helped courts navigate tricky public policy issues before.
The hearing is set to start on May 25.