A group opposed to euthanasia is encouraging more doctors to sign a new open letter objecting to assisted suicide.
But the MP backing a bid to legalise euthanasia says his bill is solid, and claimed the loud objections of some doctors were hypocritical and detached from public opinion.
The Care Alliance, which opposes euthanasia, said one its trustees, Dr Sinead Donelly, launched the online letter to send a message to lawmakers.
The letter claimed to have attracted the support of 40 doctors by mid-afternoon.
"We believe that crossing the line to intentionally assist a person to die would fundamentally weaken the doctor-patient relationship, which is based on trust and respect," the letter stated.
"We are especially concerned with protecting vulnerable people who can feel they have become a burden to others, and we are committed to supporting those who find their own life situations a heavy burden."
The letter invoked the position statements of the World Medical Association and New Zealand Medical Association (NZMA).
NZMA chairman Stephen Child said the association was not aware of the letter being published. However, the NZMA's position statement on euthanasia was recently reviewed and was consistent with the tenor of the open letter.
In its position statement, the NZMA opposed euthanasia but supported the concept of "death with dignity and comfort".
"Euthanasia, that is the act of deliberately ending the life of a patient, even at the patient's request or at the request of close relatives, is unethical."
Yet the NZMA supported the right of patients to decline treatment, or request pain relief. It also supported the right of access to appropriate palliative care.
Act Party leader and Epsom MP David Seymour said it was telling that the open letter didn't directly attack his bill.
"So I'm actually a little bit chuffed ... because it shows I have a high-quality bill."
In June, Mr Seymour lodged a new bill in the private members' ballot to legalise medically assisted suicide.
Today, he said the main challenge was getting the bill drawn, but expected this to happen next year.
Mr Seymour said that when doctors campaigned on political issues, they could be hugely influential. Yet the MP said he was confident the bill would pass, as New Zealand had a "liberal majority" in Parliament.
He said his bill was the best chance of legalising euthanasia in New Zealand, unless there was an unlikely "revolution" in the National Party caucus.
Mr Seymour said the doctors' opposition and the NZMA statement had hypocritical or inconsistent elements.
"These guys are saying it's absolutely fine for your doctor to give you a little bit too much morphine and you end up going out under those circumstances. What they're opposed to is a patient actually making an intentional choice."
The MP said his bill would not force doctors to take a role in helping patients to die.
Instead, the bill was about choice, he claimed.
Previous attempts by Michael Laws and Maryan Street to legalise euthanasia when they were in Parliament were unsuccessful.
Mr Seymour said he frequently discussed the contentious issue with Ms Street, a former Labour Cabinet minister.
But he hadn't had any contact with Mr Laws.
Care Alliance secretary Matthew Jansen said opposition to assisted suicide was growing around the world.
"Just last week, Justice Michel Pinsonnault of the Quebec Superior Court ruled that 'medical aid in dying' is simply a euphemism for euthanasia," he said.
"I am deeply grateful to the doctors who have already signed up to the open letter, and encourage others to follow their lead."
The issue of euthanasia or assisted dying sparked extensive debate this year when Wellington woman Lecretia Seales fought a High Court battle over her right to die.
Ms Seales died from an aggressive brain cancer on June 5, hours after learning that the High Court would not let her doctor help her to die without being liable to criminal prosecution.