From S&P:
In this article, we address frequently asked questions from market participants about how a potential sovereign rating downgrade would affect our ratings on Australia’s states and territories. In July 2016, S&P Global Ratings revised to negative from stable its outlooks on the ‘AAA’ rated State of New South Wales, State of Victoria, and Government of Australian Capital Territory after a similar action on the Commonwealth of Australia (see “Australia Outlook Revised To Negative On Growing Fiscal Vulnerabilities; ‘AAA/A-1+’ Ratings Affirmed,” published on July 6, 2016).
A one-notch sovereign downgrade on Australia would not affect all of its states and territories equally. In fact, such an occurrence would only affect the states and territories with ‘AAA’ long-term foreign currency ratings. In the event of a sovereign default, the economies and finances of those states and territories would be likely to deteriorate in line with the Australian sovereign. S&P Global Ratings would not downgrade the states and territories with long-term foreign currency ratings of ‘AA+’ or lower in the event of a one-notch sovereign downgrade to ‘AA+’.