Senior bishops have warned that new plans to allow homosexual marriages could destroy the "fragile unity" of the global Anglican Communion.
The Church of England leaders fear that the controversial move would go against traditional biblical teaching and have "immediate and negative consequences" for relationships with other provinces around the world, as well as the central position of the Archbishop of Canterbury.
In an official letter they also urge clergy to "maintain a critical distance" from governments and resist any moves they make to allow "gender neutral" weddings.
Their strongly-worded letter - made public on the first day of a meeting of the Church of England's governing body, the General Synod in York - comes just days after a new traditionalist group was formed to oppose the liberal direction of Anglicanism.
It highlights once again the threat to the unity of the 80 million-strong Communion posed by conflicting attitudes to homosexuality.
The latest fears have been raised over plans by the Church of Sweden, which is formally linked to the Church of England through an agreement called the Porvoo Declaration, to make its marriage liturgy "gender neutral" so that same-sex couples can have traditional wedding services for the first time.