If you make wine, import wine into Australia or sell it by wholesale, you'll generally have to account for wine equalisation tax (WET).
WET is a tax of 29% of the wholesale value of wine. It is only payable if you are registered or required to be registered for GST.
It's designed to be paid on the last wholesale sale of wine, which is usually between the wholesaler and retailer. But it may apply in other circumstances – such as cellar door sales or tastings – where there hasn't been a wholesale sale. WET is also payable on imports of wine (whether or not you are registered for GST).
(Taken from ATO website)