The South Australian Government's controversial bank tax is contained in a piece of draft legislation known as the Budget Measures Bill.

If successful, it means major banks operating in SA will have to pay a quarterly levy of 0.015 per cent on bonds and deposits over $250,000 — excluding mortgages and ordinary household deposits.

With the support of two independent members of cabinet, Labor has the numbers to get the bill through the House of Assembly.

But it's a different story in the Legislative Council, where the Government does not have the numbers.

If the Liberals, two Australian Conservative MLCs and Nick Xenophon Team representatives stick to their guns and vote against it, the bill will not pass.

What's the catch?

The Budget Measures Bill also contains other important taxation changes.

Some, like a levy on foreign real estate investors, deliver Treasury more money.

Others, like payroll tax relief and stamp duty relief for apartment buyers, are designed to hand money back.

Because the bill is a "money bill", the Legislative Council cannot amend it as it does with many others.

Instead, it can only make suggested changes — written into the bill with erased type — for the House of Assembly to consider.

What if the Government sticks to its guns?

Here's where things get really interesting. If the Government gets a recommendation from the Legislative Council to defeat the bank tax, it can either:

Fall on its sword and remove the bank levy, wearing a $370-million hit to the budget bottom line

Fall on its sword and remove the bank levy, wearing a $370-million hit to the budget bottom line Reintroduce the bill as is, in the hope of a change of heart in the Upper House

Reintroduce the bill as is, in the hope of a change of heart in the Upper House Replace the bank levy with another tax or revenue measure that may or may not be blocked

Replace the bank levy with another tax or revenue measure that may or may not be blocked Shelve the Budget Measures Bill. This will still cost the budget hundreds of millions of dollars, but means other measures like payroll tax and stamp duty relief will not go through.

For the moment, however, the Government has suggested it will stick to its guns and introduce the Budget Measures Bill as it is.

Has this happened before?

Yes, but not often. Unlike the Federal Parliament, the major parties in SA have long had a mutual understanding of sorts that governments should be able to pass their budgets in their entirety.

Opposition Leader Steven Marshall believes the public is against the levy. ( ABC News: Sowaibah Hanifie )

This convention was broken in 2014 when the Liberals, Family First and John Darley joined forces to block the Labor Government's CBD parking levy.

In that instance, the Government ended up excising the proposed parking tax from the budget and also cancelled associated spending on new park'n'ride facilities.

In this case, the Government has suggested the bank levy is funding the budget's $200 million jobs package.

In reality, however, the two budget measures are not directly tied.

Is there any other way out of this stalemate?

There's always the thermonuclear option: an early election.

For this to occur, the Government would need to declare the Budget Measures Bill a "bill of special importance".

If the Legislative Council votes down or ignores such a bill, the Government has the right to ask the Governor to dissolve the House of Assembly and issue writs for an election.

It's worth noting this is extremely unlikely.

South Australians are already due to go to the polls in March and it would be a brave Government that sought an early election to win a mandate for a new tax.

Also, as Prime Minister Malcolm Turnbull and British Prime Minister Theresa May have learnt, voters in recent times have not been particularly keen to reward governments seeking an early poll.