The Sydney Anglican diocese is set to ban same-sex weddings from any Anglican church or building, and prohibit its properties from being used to promote homosexuality or "transgender ideology".

Critics within the church say the far-reaching policy could stop pastors and teachers from speaking in favour of marriage equality, and stifle student-led LGBTI support groups at Anglican schools.

Documents obtained by Fairfax Media also reveal the church sees the current debate about its right to fire gay teachers as a "key threat" to its ability to foster a Christian ethos at its schools.

Anglican Archbishop of Sydney Glenn Davies. Credit:Kate Geraghty

The 51st Synod of the Sydney diocese will next week debate the introduction of a property policy to ensure church-owned buildings are used only for "acts or practices which conform to the doctrines, tenets and beliefs of the diocese".