For several years now, regulators have tacitly acknowledged that some businesses are gouging customers who pay on credit.

However, attempts to stamp out the excessive fees for paying on plastic are proving to be frustratingly slow.

Bit on top: an inquiry is now looking at the practice of adding a surcharge when purchases are made with credit cards. Credit:Michel O'Sullivan

Credit card surcharges – the extra fees levied on customers who use credit, instead of some other payment type – have the dubious honour of being the most complained-about issue in the last year's financial system inquiry.

An online campaign led to more than 5000 submissions being lodged about this issue. But it is not just a populist concern.