A bill currently going through the assembly proposes that everyone will be on the organ donation register unless they opt out.
But some of Northern Ireland's most senior clinicians have been warning Stormont's health committee that the bill is unhelpful and potentially damaging.
Dr Paul Glover, the regional clinical lead on organ donation, said he believes the bill "in isolation" will fail.
"It will have to be underpinned by education," he said. "We have to have society talking about organ donations, talking to family, making their wishes known.
"This is about changing society - it's not about saying this is the law, therefore this is what we must do. This is about the positivity of it, coming from society up."
Dr Glover said the wording of a section of the legislation has the potential to decrease donation rates.
"Clause 4 undermines the whole concept of deeming consent, because if, ultimately, the family has the final say, then the wishes of the deceased individual are of secondary importance."
Northern Ireland has the highest deceased donation rate in the UK, with 48 deceased donors last year.  It also ranks highly internationally.
Safeguards in the proposed legislation would mean that a 'qualifying person' - such as a friend or relative - would have to affirm that the deceased person would not have objected.
But intensive care consultant Dr TJ Trinder said there would be "no credible reason for the legislation, unless the intent is to override family objections to donation".
He said practitioners recognise that family instinct is important and must be respected.
Dr Glover said it is possible, under the proposed legislation, that if someone had not taken action to opt out and had never discussed the issue with family, then organs could be removed from someone who never wished that to happen.
The British Medical Association said it is broadly supportive of an opt-out system.
Dr John Chisholm, chair of the BMA's Medical Ethics Committee told the health committee that its members have voted consistently in favour of "a soft opt-out system with safeguards, so the majority view within the medical profession is in favour of moving in that direction."
The most senior doctor dealing with organ donation in Northern Ireland says legislation is not the way to increase donation rates.