A group of 65 health professionals has written to Jersey's health minister urging him not to make it legal for someone to take their own life.
The States will debate whether to allow assisted dying for people with terminal illness or unbearable pain during their sitting this week.
The medical professionals say it would be a "seismic change".
However, Dignity in Dying said "the vast majority" of Jersey citizens are in favour of assisted dying.
The group of health professionals also say they will not take part in any voluntary suicide if the law is passed.
It would allow both euthanasia and assisted suicide, for those with terminal conditions and incurable physical conditions.
Supporting the proposed change, Sarah Wootton, of the Dignity in Dying group, said: "73% of Jersey citizens [polled] support terminally ill and mentally competent adults having the choice.
"This is at the end of the day about choice."
The doctors' open letter, addressed to the Health Minister, said: "We are concerned about the most vulnerable members of our society who may feel coerced into a decision they would not make if the law did not permit it."
"It is very hard for clinicians to diagnose unbearable suffering or to predict time to death accurately for many conditions," it adds.
The letter concludes: "We will not participate should this be passed."
Dr Carol Davis, consultant in palliative medicine, said: "Legalising assisted suicide and euthanasia is a seismic legal, ethical and moral change and it carries serious risks to society and particularly its most vulnerable members."
Dr Tracy Arun-Castro expressed concern any legalisation of assisted dying could be extended to allow the euthanasia of children.