Some church leaders say a meeting on assisted suicide methods being held in Cardiff could be "very dangerous".
Dr Philip Nitschke had planned to demonstrate how to use a laptop connected to a lethal injection at the Quakers Meeting House on Thursday.
But members of the Catholic church said it could act as an "invitation to commit suicide".
Quakers said at their request the event would no longer include a workshop or a demonstration of how to end life.
Other workshops run by Dr Nitschke in the past week have been cancelled in Belfast and Eastbourne after the venues decided not to go ahead.
Dr Nitschke, who founded euthanasia group Exit International in 1997, said the purpose of the public meeting was to educate people about having a peaceful death.
The Australian physician had planned to stage a demonstration of his new "deliverance" voluntary euthanasia machine.
The device is a laptop computer connected to a syringe that injects a lethal substance if the patient correctly answers a series of questions.
He said: "It makes sense for every person to develop for themselves a strategy so they can end their lives peacefully if they find themselves in a situation where they have no control.
"I will be explaining why this makes sense within UK law where somebody can be prosecuted for assisting suicide and that's where my laptop device comes in.
"In the closed session, I will explain how to get hold of the relevant drugs and what gives you a peaceful and reliable death."
But in a statement on Wednesday evening, the Quakers, who are providing the meeting room for the event, said it had been changed at their request.
"At our request, Exit International have modified their plans for the event and it will no longer include a workshop," the statement read.
"Exit International have assured us that no apparatus for ending life will be present, nor will they be demonstrated or shown on film."
"Quakers in Cardiff are not hosting this event. Allowing a commercial letting does not imply that we agree with the views of the organisation. Our premises are hired by a wide variety of groups as a general reflection of Quakers' long held belief in the rights of everyone to express diverse opinions.
"Quakers respect life and we would therefore have concerns if people were being exploited or pressurised. We would not allow an event on the premises which breaks the law."
Speaking before the event was amended, Monsignor Robert Reardon, administrator for the Catholic archdiocese of Cardiff, said the it raised "serious concerns".
He told BBC Wales: "Assisted suicide is not something we would support and not something we would recognise as a morally valid option.
"I think the whole thing with the laptop is very, very dangerous because it can be seen as an invitation to commit suicide and, depending on the state of minds of vulnerable people, it can then be viewed as a valid option."
Also speaking before the event was amended, Canon Peter Collins, dean of the Cardiff Metropolitan Cathedral of St David, which is just a few doors away from the Quaker meeting house, shared the view that the seminar was "dangerous".
He said: "I think the decision by the Quakers to allow this event to take place is disappointing.
"Our first concern must be the potential for vulnerable people being influenced."
There was also concern from within the Church in Wales.
The Bishop of Monmouth, the Right Reverend Dominic Walker, said he welcomed the debate about assisted suicide but was concerned that the terminally ill or severely disabled would be seen as a burden on society and feel under pressure to opt for it.
"Whilst assisted suicide may be viewed as the most loving thing to do in some circumstances, there would need to be safeguards so that it was not used as justification in most circumstances and I am not convinced from the draft legislation that I have seen that this would necessarily be the case."
The Safe Exit Workshop will be held at the Cardiff Quakers Meeting House in Charles Street on Thursday.
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