Some doctors are set to argue against moves towards an organ donation system of presumed consent in the UK.
Under presumed consent all people are assumed to be willing to donate their organs unless they have opted out.
No part of the UK has introduced such a system yet, although the Welsh assembly favours the idea.
However, delegates at the British Medical Association's annual conference in Cardiff will debate later whether the move could damage trust in doctors.
Those in favour of presumed consent, which has been supported by the BMA for the last 10 years, believe it would help boost UK donation rates, which, despite recent improvements, still lag behind many other countries.
More than 3,700 donations took place last year - a 5% increase on the previous year - but there are still about 8,000 people on the waiting list for transplants.
Over the last three years, the NHS has invested in specialist nurses and transplant co-ordinators to identify potential donors and allow for approaches to families when death becomes likely.
Dr Sharon Blackford, a dermatologist from Swansea, who is proposing the motion calling for the BMA to change its position, believes this investment should be built on.
"[Donation] rates are going up and I and my colleagues are concerned that if we move to presumed consent it could damage trust in doctors. If someone is in intensive care, families may feel doctors just want to harvest the organs," she said.
"It also goes against the whole idea of the moment - putting patients in charge. People may start thinking about it differently and it could turn people off."
Dr Blackford will cite the experience of Spain where organ donation hardly changed following the introduction of presumed consent in 1979.
But Professor Vivienne Nathanson, head of science and ethics at the BMA, said other countries had seen a positive effect.
The BMA's backing of presumed consent is on the basis that it has public support and that families are in agreement.
"I don't think it goes against patient choice. They can still opt out. One of the problems now is that people who want to donate sometimes don't tell their families. But with presumed consent you would have a public campaign and it would get people discussing the issue."
She also said that under the BMA's current position, the family would still be consulted and, if they had reservations, their wishes would be respected.
"It will strengthen trust if anything," she added.