This week will see another turning point in Australia’s marriage equality saga when the high court hears arguments in a challenge to the government’s postal vote. The high court could deliver its verdict as early as Thursday so it’s timely to consider what the challenge is about and what will flow from the court either upholding or striking down the postal vote.

There are two cases against the postal vote. The first, which I helped organise, is from Parents and Friends of Lesbians and Gays, and lesbian mum of three, Felicity Marlowe. They are concerned about the platform a postal vote will give to hate. This case also involves the Tasmanian independent Andrew Wilkie, who has a history of challenging government overreach.

The second case is from Australian Marriage Equality and the Greens LGBTI spokesperson, senator Janet Rice. Our case broadly argues that the postal vote is an unconstitutional overreach by the government because it is spending money without parliament’s approval.

Both cases argue the specific point that the power the government has used – a law allowing the finance minister to spend money on things urgent and unforeseen – is not appropriate because a postal vote is neither urgent nor unforeseen. It’s true that marriage equality is urgent, but there’s nothing urgent about surveying the community on it. There’s also nothing unforeseen about a postal vote because cabinet ministers have been discussing it since the beginning of the year.

The government’s defence to these points is essentially that it decides what is urgent and unforeseen because it is the government. That may seem pretty weak, but we should not assume the court will rule against the government. The case will come down to constitutional questions about the power of the executive branch of government in relation to parliament.

I thought these questions were largely settled when King Charles I had his head chopped off, but apparently there is still unsettled law about them in Australia. The divine right of finance ministers might still carry the day. If the court does rule for the government, the nation will erupt into a full-throated marriage equality debate.