Christian Concern leader Andrea Williams has expressed her disappointment over changes to a Lambeth Call on marriage and sexuality.
The Call on Human Dignity will be discussed and voted on by 650 Anglican bishops at the Lambeth Conference next week.
It has been revised to remove a reaffirmation of the 1998 Resolution 1.10, which upholds marriage as a union between a man and a woman, and rejects homosexual practice.
The change was made after pressure from liberal bishops, including those in the US Episcopal Church and Church in Wales.
Ms Williams, a former lay member of the Church of England General Synod for 10 years, said that the views of traditionalist Anglicans were being silenced.
She said that "apostate" bishops should be removed from their positions.
"Faithful Anglicans around the world stand on the biblical principle of marriage between a man and a woman as taught in Scripture, reflected in the doctrine of the church throughout history and re-stated in Lambeth 1:10," she said.
"Their voice is being silenced by a vocal and powerful minority of apostate Western and American Bishops.
"These bishops that deny the gospel should be removed from their positions rather than be allowed to use their influence to bully faithful Anglicans out of the space that is rightfully theirs.
"It is a great disservice to the gospel, its power and witness when Lambeth Palace allows this to happen."