A leading American rabbi has accused the London Beth Din of "sentencing people to death" for saying that organ donor cards are unacceptable for Jews to carry in their current form.
Rabbi Moshe Tendler, a medical ethics professor at New York's Yeshiva University, criticised long-awaited new guidelines on organ donation issued by the Beth Din and Chief Rabbi Lord Sacks.
But some senior Orthodox doctors in the UK welcomed the statement from Lord Sacks and his dayanim as a move to encourage more Jews to become organ donors.
The guidelines say that national organ donor cards would become acceptable if they carried a religious conscience clause to reassure Orthodox families that any organ donation complied with Jewish law.
It was "imperative" for families considering whether to allow the removal of an organ from a relative to consult a "competent halachic authority" first, they said.
But Rabbi Tendler believes that the conditions under which the Beth Din is prepared to permit donations are too restrictive.
According to the London Beth Din, an organ should only be taken from a person if their lungs and heart have stopped ("cardiorespiratory death").
But Israel's chief rabbinate and some American rabbis also accept the validity of "brain-stem death", when a person's heart may continue beating because they are on a ventilator. This is significant because some organs can only be taken while the blood still
The Beth Din's conditions would mean that an observant Jew could donate kidneys, livers or corneas, for example, but not heart or lungs.
Rabbi Tendler declared: "The Beth Din must realise they have sentenced to death anyone waiting for a vital organ transplant."
He said that brain stem death was "the only accurate method to determine that a patient has died".
The British Medical Association said it was "a matter of urgency for the Chief Rabbi to meet organ donation experts to discuss how to maximise donations that they consider compliant - otherwise the number of donations available may be restricted".
Anthony Warrens, Imperial College professor of renal and transplantation medicine in London, supported the Beth Din move. "Too many of my patients have suffered and died for a lack of a transplant. I hope that this important declaration from our rabbinic leaders will contribute to making that a thing of the past," he said.
But Daniel Braunold, an Orthodox doctor who has lectured on medical ethics, said he was "disappointed" by the guidelines, which he felt represented a "lacklustre and weak decision that pedals backwards in time".
The Beth Din statement did not go into whether a Jewish patient should receive an organ only if it came from a donor pronounced dead according to the cardiorespiratory rather brain-stem definition.
That was a "spurious question", the Chief Rabbi said on Wednesday. The only question was whether the organ was "given freely by the consent of the donor".
Lord Sacks said that as soon as national donor cards were able to meet halachic requirements, he would carry one himself.
He declared: "We feel the best way forward is that we should inform the community there are voices this way, there are voices that way. If they want the view of the London Beth Din, it is this, but ultimately there's a matter of individual conscience."
But the guidelines were also criticised by Robby Berman, director of the American-based Halachic Organ Donor Society, whose donor cards are endorsed by leading Orthodox rabbis, but not by the London Beth Din.
Mr Berman said: "I don't understand the moral sensibilities of Rabbi Sacks issuing a declaration that encourages Jews not to donate organs upon brain death, but does not forbid Jews from taking organs from gentiles who are brain dead. If a Jew who is brain dead is alive, is not a gentile who is brain dead similarly alive?"
The Beth Din says that the National Organ Donor Registry has been asked to explore changes in the registration system that would allow Jews to record their religious wishes. Until then, donor cards, "even those purporting to be halachic", were "unacceptable", according to the guidelines.
A number of United Synagogue and other Orthodox UK rabbis, however, are understood to have recently signed up for donor cards.
Both the Reform and Liberal movements accept brain-stem death.