Those backing the End of Life Choice Bill are confident the bill's second reading will pass this week, despite pushback from doctors.
Over the weekend, an open letter signed by more than 1000 doctors declared that even if legalised, euthanasia is unethical.
The bill, which gives people with a terminal illness the option of requesting assisted dying, is due to have its second reading on Wednesday.
The Care Alliance, a charity that opposes physician-assisted euthanasia, took out a full-page ad in the Herald on Sunday to post the letter.
But ACT Party leader David Seymour, who introduced the bill, said it will likely pass on Wednesday and the contents of the letter are not new.
"This represents 6 percent of New Zealand's doctors, all of whom will have the right to opt out if the End of Life Choice Bill becomes law, what they don't have a right to do is deny choice to all of those New Zealanders who do actually want it," he said.
But palliative care specialist, Dr Sinead Donnelly, who organised the letter, said the bill changes the relationship between a doctor and their patient.
Dr Donnelly said she had a message for MPs voting on Wednesday.
"As doctors we don't want to be part of it, you're going to, in our view, destroy the profession of medicine by drawing us in to ending the life of our patients.
"The risk to the vulnerable is much too great," she said.
Medical Association chair Dr Kate Baddock agreed with the letter and the majority of their more than 5000 members oppose euthanasia.
Dr Baddock said their stance was in line with the international response.
"In the World Medical Association, some 119 countries belong and over 90 percent of them are completely against euthanasia and physician-assisted suicide," she said.
If New Zealand was to adopt assisted dying, Dr Baddock said the Medical Association will be advocating for a policy like Switzerland, where doctors are not involved in the process at all.
With more than 16,000 doctors in New Zealand, the End of Life Choice Society of New Zealand president, Dr Mary Panko, said there will be enough doctors prepared to carry out assisted dying.
"There was a poll done last year which showed that about 37 percent of doctors in New Zealand support medical aid in dying, doesn't mean they would all take part, but there is going to be plenty for the small numbers initially that would be willing to take part in the procedure," she said.
Dr Panko said Wednesday's vote looks as if it will go in their favour, but then it will get to the difficult part, where the bill will be debated bit by bit in Parliament before its third and final reading.