The appointment in America of an openly gay bishop will have grave repercussions for the Anglican Church in the UK and worldwide, warn clerics.
The evangelical group Reform says the appointment is a warning to the Church of England.
The Church Society - which represents Anglicans who emphasise the primacy of the Bible - said it could precipitate a crisis which could split the Church.
The American Episcopal Church's House of Bishops is due to vote on the confirmation of Reverend Canon Gene Robinson of New Hampshire to serve as a bishop.
The House of Deputies - made up of clergy and lay people - has already decided by a substantial majority to approve the appointment.
But conservatives and have warned the decision will alienate the Episcopal Church in the States from the worldwide Anglican Communion.
And religious leaders in the UK have said it could end up splitting the Church of England.
Reverend David Phillips, general secretary of the Church Society, challenged the Archbishop of Canterbury, Dr Rowan Williams, to say exactly where he stood on the appointment of the gay bishop.
"He should show leadership on this issue," he said. "He has said he would not intervene in other provinces, but I would hope he would say it should not go ahead because it is wrong.
"People want to know where the Church of England stands. I would like him to say that, because of its decision, the Episcopal Church in America is no longer a part of the Anglican Communion."
Mr Phillips said it might be a good thing if the issue came to a head once and for all, and the Church did actually split over the appointment of gay priests.
"It might actually be a good thing if it did split," he said. "The only churches which are actually growing are the ones which know where they stand on this issue."
"Certainly, we consider what the Episcopal Church in America has done is entirely wrong, and totally against the historic Christian church and the scriptures."
Reform is equally damning of the likely appointment.
Schismatic
Reverend Rod Thomas said it would produce a schism among Anglicans.
The Church of England would have to decide whether it would "faff around" and still accept the Episcopal Church in America as part of the Anglican Communion, or whether it would ostracise it.
"This is unilateral action by a church that has largely developed to be schismatic.
"To some extent, what happens will depend on the worldwide reaction, whether people will faff around about the issue or try and take action and boycott them."
"But there will be a split in the Episcopal Church in America and this will be a warning signal to us in the UK because the split will also come here."
But the Dean of Guildford, the Very Reverend Victor Stock, said that the Church of England was being hypocritical.
He told BBC News 24: "In England we do have gay bishops and gay senior people in the churches but we don't say anything about it because we would rather not, you know, say anything in public.
"I think the American example is of much more openness and honesty and being sensible and not so hypocritical."
A spokesman for the Church of England said that the Archbishop of Canterbury had no intention, as yet, to issue a statement as the gay appointment was considered an internal matter for the Episcopal Church in the United States and the decision had still to be ratified by its House of Bishops.
However, Dr Rowan Williams had sent a private letter to the primates of the Anglican Churches worldwide, expressing his concern on the matter, he added.
The Church of England has been mired in controversy recently over the appointment of a celibate gay priest Canon Jeffrey John to the post of Bishop of Reading.
Dr John later withdrew after a storm of protest, apparently at the behest of Dr Williams.