The War on Cash by James Reed

Here is a worrying sign from India, reported by Brian Maher at http://dailyreckoning.com/author/bmaher, November 17, 2016.
In India 90 percent of all transactions are by cash. But the government, in a plan so secret that even India’s financial institutions were unprepared, suddenly banned its 500-rupee and 1,000-rupee bills, worth $US 7.50 and $US 15 respectively. This led to poor people having to go back to barter, if they could.
This shows that governments could outlaw cash overnight, even in Australia. However, willing members of the legal profession could immediately initiate action in our High Court of Australia to pull the federal government back to order using our constitution as the supreme law of the land.

From Wikipedia:
https://en.wikipedia.org/wiki/Section_51(xii)_of_the_Constitution_of_Australia

Section 51 (xii) is a subsection of Section 51 of the Constitution of Australia that gives the Commonwealth Parliament the right to legislate with respect to “currency, coinage, and legal tender.”

Generally, powers in section 51 of the Constitution of Australia can also be legislated on by the states, although Commonwealth law will prevail in cases of inconsistency. However, the currency power must be read in conjunction with other parts of the Constitution of Australia. Section 115 of the Constitution establishes “a state shall not coin money, nor make anything but gold or silver coin a legal tender in the payment of debts”. This section effectively makes the concurrent power in section 51(xii) exclusive to the Commonwealth.