Police in Wellington are being accused of running an illegal moral crusade targeting elderly supporters of euthanasia.
Yesterday police admitted they used a breath-testing checkpoint to identify and trace people who had been at an Exit International meeting in Lower Hutt earlier this month.
Shortly afterwards they announced they had reported themselves to the Independent Police Conduct Authority.
The acting Wellington District Commander, Paul Basham, said police carried out the operation "in good faith", but were also aware of public concern about the legal basis for the checkpoint.
Human rights lawyer Michael Bott said officers misused used their power under the Land Transport Act, which allowed them to stop people, ask for licences and carry out breath tests for road safety.
"What you've got is New Zealand police undertaking what appears to be some kind of moral crusade on spurious grounds to such a degree that they're prepared to use 'stop and questioning' powers under the Land Transport Act for ulterior motives, which seems completely improper."
In their defence, police said they had a responsibility to investigate any situation where they had reasonable grounds to "suspect that people are being assisted in the commission of suicide".
But Mr Bott said police had no right to intervene in the way they did.
"The mere fact that you attend a meeting with a group who believe in the right to commit suicide in certain circumstances - if you're unwell or terminally ill - doesn't mean you actually endorse those aims, or that in fact you're contemplating assisting someone with bringing about their own demise.
"So you really haven't got good cause to do that."
Otago University law professor Mark Henaghan agreed the officers had acted unlawfully.
"Under the Bill of Rights Act, there is a provision that people should not be unlawfully detained. They [the elderly people] weren't detained in the sense of being put in a cell but they were detained, and they were stopped and questioned, and were asked to hand over their licence," he said.
"The police have no more power than I have to stop someone and say 'I want to see your licence', unless they're using (their power) for the purpose it was designed for, which is the blood alcohol purpose.
"They're really not using power that they have, so they're effectively detaining people. If you haven't got the power to do it then it's illegal detention."
Wilhelmina Irving, one of the elderly Wellington people who went to the meeting, missed the checkpoint, but got a visit from a plain clothes officer anyway.
She was one of a group of elderly women visited by the officers who questioned them about their connection to the pro-euthanasia activists.
She said the ordeal had made her lose faith in the police.
"You don't think like that of the police, you think of them as trying to help people, not making things difficult for elderly people really."
The president of the Voluntary Euthanasia Society, Maryan Street, said it was unacceptable.
"The police have shown by this action how very confused they are about their own powers. You are not meant to gather information ostensibly for one purpose and then use it for another.
"That is not in their brief and that is against the laws that govern their own conduct."