The Administrative Appeals Tribunal has affirmed that the GST treatment of credit card surcharge fees, imposed by a supplier when payments are made by credit card, depend on the GST characterisation of the underlying supply.

In other words, if an underlying supply is GST-free, the credit card surcharge fee will be GST-free. Conversely, where the underlying supply is a taxable supply, the fee will attract GST.

A good example would be the Qantas credit card charge on an airfare booked on the internet.  If the fare is an international one, then the fee will not include GST; if the fare is a domestic one the fee will include GST.