The Church of England's national assembly will begin a key three-day meeting on Monday where members will be asked to give final approval to legislation introducing women bishops.
The 470-strong body, meeting in Church House, London, will vote tomorrow on whether to allow the legislation to clear its final hurdle before going to the Houses of Parliament for approval.
The decision is billed as the biggest the General Synod has taken in the 20 years since it first backed the introduction of women priests.
In spite of women now making up around a third of all clergy, and just under half of those training for ordination, the Church has struggled to draw up legislation introducing women bishops which is accepted by both traditionalists and pro-women campaigners.
Complex negotiations have centred on the arrangements where a woman bishop is appointed but traditionalist parishes reject her authority.
Under the draft legislation before the General Synod, a woman bishop would delegate to a stand-in male bishop to minister to an objector parish by reference to a code of practice.
The legislation has been backed by 42 out of the 44 Church of England dioceses but needs a two-thirds majority in all three houses of the General Synod - of bishops, clergy and laity - to gain final approval.
Commentators have said they believe it will clear the houses of bishops and clergy with the necessary two-thirds majority but the outcome among lay members of the General Synod is thought to be on a "knife-edge".
More than 1,000 Church members, including bishops, clergy and senior laity, have signed an open letter urging the Synod to vote in favour of women bishops.
The letter, published in The Independent on Monday, says: "Just as the Churches have repented of our historic anti-Semitism and endorsement of slavery, so we believe that we must now show clearly that we no longer believe women to be inferior to men."
Tuesday's vote will test the authority of both the outgoing Archbishop of Canterbury Dr Rowan Williams, and the Rt Rev Justin Welby, Bishop of Durham, who will succeed him. Both clerics have urged the General Synod to vote for the legislation.
If approval is given tomorrow, the legislation will go to the Houses of Parliament before receiving Royal Assent, paving the way for the first women bishops in 2014.
Other topics to be debated by the General Synod include the living wage and youth unemployment. Members will also bid farewell to Dr Williams, who leaves after a decade in the post at the end of this year to become Master of Magdalene College, Cambridge.
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