The official Anglican Church of Australia is not a "monolithic" structure. Its structure and some legal issues around its governance were helpfully set out in a decision of Hammerschlag J in the NSW Supreme Court in 2015:
[2] The Church has a highly formalised governance structure. It is organised into geographical areas, each called (in one of its meanings) a diocese. Each diocese is the see of a bishop. There are 23 dioceses in Australia... Dioceses are organised on a provincial basis. Apart from Tasmania (which for historical reasons is treated separately), each Australian State corresponds to a Church province. Each diocese comprises smaller geographical areas called (in one of its meanings) parishes, within which there must be at least one licensed or consecrated church...
[3] Nationally, governance of the Church resides in a committee known as General Synod, presided over by a bishop designated the Primate.
[4] The Diocese is governed by its own Synod, which has a term of three years and meets at least annually...
[6] At no level does the Church itself, as an institution, have corporate existence. It is a series of unincorporated voluntary associations at different levels: national, provincial, diocesan and perhaps even parish.
Anglican Development Fund Diocese of Bathurst in its own capacity and in its capacity as trustee of the Anglican Development Fund Diocese of Bathurst (receivers and managers appointed) --v-- The Right Reverend Ian Palmer, Bishop of The Diocese of Bathurst; Commonwealth Bank of Australia --v-- The Right Reverend Ian Palmer, Bishop of The Diocese of Bathurst [2015] NSWSC 1856 (10 December 2015) (the Bathurst Diocese case), per Hammerschlag J, [2]-[6].

Each diocese of the ACA has a high degree of autonomy in the way that it operates, but each is meant to be bound by the Constitution under which all have agreed to operate. (While the Church as a whole is not an "incorporated" body, State and Territory law has implemented the Constitution as part of laws recognising the rules therein as governing property matters. In NSW, the Anglican Church of Australia Constitution Act 1961 (NSW) incorporates the ACA Constitution into a Schedule, and the Act itself provides in section 2 that the Constitution has legal effect "for Church property purposes".)

In recent years there has been a debate within the ACA as to the extent to which the Anglican Church can recognise, or bless, or even solemnise, same sex marriages. The traditional view of the Bible's teaching is only marriages between a man and a woman represent God's purposes for humanity. When Australian law was changed to allow same sex marriages, the changed legislation made it clear that ministers of religion would not be obliged to conduct same sex wedding services: see my blog comment in December 2017 on the general issues, and section 47 of the Marriage Act 1961 (Cth) (sections 47A and 47B also provide further religious freedom protection in this area.)

As well as the general law of the land making it clear that ministers of religion can decline to solemnise same sex marriages, within the ACA a resolution of its General Synod in 2017 affirmed that:
the doctrine of our church, in line with traditional Christian teaching, is that marriage is an exclusive and lifelong union of a man and a woman.
See 'MARRIAGE, SAME-SEX MARRIAGE AND THE BLESSING OF SAME-SEX RELATIONSHIPS',
adopted 7 Sept, 2017, at https://anglican.org.au/the-general-synod/search-resolutions-of-gssessions/?sid=2827.
But in more recent days a number of bishops have expressed their wish, not to directly contravene this statement by solemnising same sex marriage, but to allow a "service of blessing" to be provided in the church to same sex couples who have married under the general law. Over the objection of a majority of Australian bishops, the "Appellate Tribunal" of the church ruled on 11 Nov 2020 that providing such blessings would not be contrary to the "doctrine" of the church and hence not inconsistent with the ACA Constitution.

I commented on this earlier this year: see "Blessing same sex marriages in the Anglican Church in Australia" (April 5, 2022), with a link there to a chapter I had provided to a collection of comments on the matter prepared before the most recent General Synod. In my view it seems clear that the doctrine of marriage was a matter that fell within the definition of "doctrine" in the ACA Constitution. To "bless" a same sex union is not simply to express support for the two parties as members of the church, but provides an expression of approval of homosexual physical intimacy. This is contrary to the teaching of the Bible, and also the "Book of Common Prayer", long seen as one of the primary sources of Anglican theology.

The most recent General Synod of the ACA was held in May 2022. While there was a motion accepted that "there is currently no liturgy for the solemnisation of a same-sex marriage", a 12-10 majority of the "House of Bishops" refused to support a motion that sought to affirm that marriage is only between a man and a woman and the blessing of same sex marriages was not in accordance with the teaching of Christ. This was seen as a watershed moment for some Anglican parishes who had been looking for an affirmation of Biblical teaching from the leadership of the ACA.

International context

The fact is, of course, that debates of this sort have certainly not been confined to Australia. The wide-spread social acceptance of same sex marriage across the Western world, and parts of the world influenced by the West, has seen these sort of debates in many areas. A movement of Bible-based Anglican churches which has taken the title GAFCON (founded after a 2008 conference in Jerusalem called the "Global Anglican Futures Conference") has now been established. Some Anglican dioceses aligned with GAFCON are those in fellowship in the world-wide Anglican communion centred on the Archbishop of Canterbury. Others are structures that have developed when evangelical Anglicans left historic Anglican institutions which had changed their teaching to accommodate same sex relationships. In North America, for example, the Anglican Church in North America is now operating, composed of many churches and dioceses which have realised they can no longer be in fellowship with the Episcopal Church.

Recent developments

GAFCON Australia is an organisation of evangelical Anglicans in fellowship with the broader GAFCON movement. The members of the organisation, until recently, were all part of the mainstream Anglican Church of Australia, but committed to maintaining a witness to the truth of the Bible within that organisation. The Chair of the Board is the Rt Revd Dr Richard Condie, who is the ACA Bishop of Tasmania.

It was at the recent GAFCON Australia conference in Canberra that the announcement was made that the Diocese of the Southern Cross would commence operation, to provide an alternative episcopal structure for Anglican parishes in Australia who could no longer operate under an ACA bishop who had moved away from the teaching of the Bible. The first parish to be established is a congregation in Beenleigh in Brisbane, which under their rector Peter Palmer has left the ACA diocese and started meeting in a local RSL club.

The legal implications of this new diocese remain to be worked out. Formally the "Diocese of the Southern Cross" is the "Diocese of the Southern Cross Limited", a company limited by guarantee. (Its registration with the Australian Charities and Not for Profits regulator can seen here, along with its constitution.) That it has chosen a corporate structure of this sort is not unusual. There are many complications created by the fact that (as noted above by Hammerschlag J) the mainstream ACA is an "unincorporated association" (I noted some of those complications in an article about the case cited above, where the Commonwealth Bank was suing the then Bishop of Bathurst to recover a loan made to the diocese.) It seems sensible to start out with a corporate structure.
Information provided so far by the new Diocese indicates that they will expect Anglicans seeking to find a home there to leave behind their ACA congregation and (presumably) any building associated with it. A "Frequently Asked Question" on their website says:
Will dioceses or parishes leave the Anglican Church of Australia to join the Diocese of the Southern Cross?

No. Some people (rather than dioceses or parishes) will leave the Anglican Church of Australia. https://scd.org.au/faqs/

But while this is the current situation, matters may become more complicated in the future. Much will depend on the way in which church properties are held. Many are owned by property trusts, some of these set up by legislation. But there may be local charitable trusts affecting individual parish properties. This was an issue which had to be dealt with by Hammerschlag J in the Bathurst Diocese Case mentioned previously from [411]- when considering whether money lent to the Diocese could be recouped, his Honour had to consider whether the trusts on which specific properties were held could be used for the purpose of relieving Diocesan debt. Whether the solution adopted in that case (that legislation allowed the Diocese to unilaterally vary the terms of such trusts if needed) is correct or not is a matter I discussed in my article on the decision.

Overseas there have been a number of cases in North America on the question whether a property owned and developed by many years by an evangelical congregation, could be "resumed" by a "progressive" diocese when the congregation resolved to leave the diocese. This 2021 article reviews a number of the cases in the US, many of which are still continuing after the Supreme Court there declined to hear appeals from States with differing approaches.
There have been few such cases so far in Australia, but there may be more in the future. The High Court of Australia in Attorney-General (NSW) v Grant ("Presbyterian Church case") [1976] HCA 38; (1976) 135 CLR 587 had to consider issues arising out of the formation of the Uniting Church of Australia from other denominations, and concluded that the specific legislation governing the union allowed the new body to operate under doctrines which were different from those that the Presbyterian Church had operated under. But it did not deal in any detail with the position of individual congregations leaving the main denomination.

More recently, in ROWE -v- THE ROMAN CATHOLIC ARCHBISHOP OF PERTH [No 2] [2022] WASCA 28 (4 March 2022), the Western Australian Court of Appeal declined to provide a remedy to a "breakaway" parish of the Roman Catholic diocese of Perth, which had been given permission to provide a "Latin Mass" by a former archbishop, but whose property was then being taken away.

It may be that in the future such disputes will become more common. Where money and resources have been directed to developing a church building being used for the proclamation of Biblical teaching, it may be argued that such real estate should not be claimed by those who want to move away from that teaching. At any rate it seems clear that the new Diocese of the Southern Cross will be aiming to provide a place of fellowship in accordance with historic Anglican principles, for Australian Anglican congregations who find that their local ecclesiastical authorities are moving away from that standard.

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