I agree it was pretty slimey. They've obviously made a policy decision effective 1 March to disallow ATO spend on all customers cards - without warning.
Here are the T&Cs for the reward program:
http://www.citibank.com.au/global_d...CitiBusiness_Rewards_Terms_and_Conditions.pdf
The key bits seem to be:
Eligible Transaction means any Retail Purchase
which is made by the use of a Card or any
other means permitted by Citibank excluding
(but not limited to) transactions by way of
Cash Advances, Balance Transfers, Special
Promotions, fees, purchases of foreign currency
and travellers cheques, foreign exchange and
ATM/ bank charges, interest charges, finance
charges, government charges, insurance charges,
payments to Citibank loan accounts (mortgage
etc), and all other transactions if the Account is
more than $10,000 in credit.
Despite being capitalised "Retail Purchase" is not a defined term.
I've made a complaint to Citi and they promise a response within 7 days. I'm minded to argue I should have my 40,000 points because they changed their interpretation of Retail Purchase without warning.