A law change to enforce anyone's wish to become an organ donor after they die will be debated by MPs this week - but doctors intend to fight the "unenforceable" bill.

National MP Jackie Blue's controversial private member's bill, aimed at boosting New Zealand's low rate of organ donation, will be introduced to the House on Wednesday.

It is certain to pass at least its first vote - to take it to a select committee for detailed consideration - as Labour has agreed to that initial support.

But it will encounter strong opposition from doctors.

The bill would create an opt-on database of people who, on the basis of informed consent, wished to become organ donors. They could state which organs they wished to donate.

The legislation would also prevent anyone from overturning the wishes of a registered organ donor.

At present, hospital staff comply with the wishes of family when a potential donor dies in circumstances where their organs could be used for patients needing a transplant.

Some transplants can use live donors, but last year only 29 people became organ donors after they had died. The shortage of donors means that some patients die waiting for a transplant. New Zealand's donor rate is one of the lowest in the West.

An audit published in 2002 found that of 104 New Zealand patients who could have been organ donors, 38 were. Of the rest, 31 families refused consent and 35 families were not asked.

Dr Blue, who has discussed her bill with intensive care specialists and transplant surgeons, acknowledged its flaws last night, saying it needed refinement at a select committee.

"The end point is to increase donor rates in New Zealand. Whatever is going to do that, let's work with it. If it's not this bill, that's fine."

Bill co-author and organ donation campaigner Andy Tookey, whose 4-year-old daughter Katie will eventually need a liver transplant because of a rare disorder, said change was needed since the donor part of driver's licences was not legally binding.

Consequently, when a person became brain dead and a potential donor in hospital, the family were consulted, Mr Tookey said. If just one relative objected, the person's organs would not be taken, even if they had wanted to be a donor.

Intensive Care Society vice-president Peter Hicks, of Wellington Hospital, said the group opposed the bill for reasons he declined to explain in detail before Wednesday's debate.

"There is a process under way to review the appropriateness and form of an organ donor register. This process should be allowed to be completed without further legislation pre-determining the result."

Auckland City Hospital intensive care specialist Tony Smith said the bill was unworkable and unenforceable in its current form.

"Very few doctors would enforce organ donation, even if the patient had signed a register, when faced with a grieving family who are opposed to it."

Organ donation was a gift that relied on public goodwill, he said. Overriding a family's wishes would endanger that goodwill, with a consequent loss of donors.

Auckland surgeon Professor Stephen Munn, director of the New Zealand Liver Transplant Unit, said overseas research on voluntary organ donor registers had shown that when told of a deceased relative's wish to donate, 95 per cent of families agreed.

Organ donation

* 29 people became donors after they died last year.
* This was New Zealand's lowest number in more than a decade.
* Around 1.1 million people have said "yes" to organ donation on their driver's licence.
* 95 per cent of families agree to organ donation from a dead relative if the person had stated a wish to be a donor, according to overseas research.
* If the person's wishes were unknown, 50-60 per cent of families agreed to donation.
* Around 350 people are waiting for a transplant, mainly kidneys, but also corneas, lungs and other organs.