The Anglican Church could split if a homosexual is appointed bishop of Reading, senior clerics have warned.
Dr John is due to become Bishop of Reading in October
Thirty-five church leaders urged openly gay Canon Jeffrey John to withdraw his acceptance of the position when they met in Oxford on Wednesday night.
"This appointment flouts the mainstream Anglican teaching on human sexuality," the leaders said in a statement issued after the meeting.
"We believe that if he is consecrated, the unity of the Church of England and
Anglican Communion will be disrupted."
Dr John was appointed by Bishop of Oxford, the Right Reverend Richard Harries, and is due to be consecrated in October.
The appointment has opened a growing divide, but the Archbishop of Canterbury Rowan Williams has said he raised no objection.
Among the church leaders to attend the Oxford meeting, called the New Network Anglican Mainstream, were Archbishop Drexel Gomez of the West Indies, Gregory Venables, presiding bishop of the southern cone - the Anglican Church in southern Latin America, five bishops from the Oxford Diocese and representatives of the American Anglican Council.
The Archbishop of Canterbury is to ordain Dr John
Members of the Church of England Evangelical Council and the conservative group Reform also attended.
A Diocese of Oxford spokesman said he was concerned that the formation of the group represented the first move towards a division of the Church.
"It could be assumed that this is the start of a break-away group.
"It could be misread that anyone who is not part of that group is not part of the main Anglican Church," he said.
But Anglican Mainstream spokesman Chris Sugden said they were not a break-away group.
"We are not leaving", he said.
Dr Harries said he wanted to see a more "gay and lesbian friendly" Church and the appointment of the gay priest was now a matter of "integrity."
"Jeffrey John has become a symbol for some people of where they don't want the Church of England to go and for others of where they do want the Church of England to go, to be much more accepting and affirming of gay and lesbian people in the life of the church," Dr Harries said.
Dr Williams earlier attempted to calm the row and pre-empt a possible schism in the Church.
In a letter to be sent to all the bishops of England, Dr Williams said on Monday: "So far as my own involvement is concerned, you should know it is an appointment I have neither sought to promote nor to obstruct".
He suggested the appointment did not mean a "unilateral" change in policy on gay bishops.