Two Otago psychiatrists are calling on their colleagues to reject euthanasia, claiming doctors are not there to kill.
The pair have been studying overseas trends and believe assisted dying unfairly impacts the most vulnerable.
"The End of Life Choice Bill, if passed, will be a rupture of the therapeutic contract between physicians and patients," said Otago University psychiatrist Yoram Barak, from the Department of Psychological Medicine.
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Barak and his colleague Christopher Gale, a consultant psychiatrist, have been examining trends in countries where similar laws have been introduced. They believe the impact is greatest on the most vulnerable.
"The people who are actually dying tend to be old or disabled, and/or poor," Gale told Newshub.
They are also echoing concerns that restrictions could be loosened over time.
"Once we pass that law, there is no going back. We've crossed that rubicon, we're in trouble," said Barak.
"They're challenged in the courts, they're described as discriminatory," said Gale.
The bill's sponsor, ACT Party leader David Seymour, says that is something the courts say Parliament must decide.
"If New Zealanders could challenge the law through the courts, the Lucretia Seals case would have succeeded and we wouldn't be here," said Seymour.
Seymour believes opponents are running out of arguments.
"This is a choice that many New Zealanders want. It's frankly disappointing to see academics at the University of Otago bringing up arguments that have been raised many times before and have been debunked by the international evidence."
A final vote on the End of Life Choice Bill is expected next month.