A powerful union representing retail workers says systems for employees to clock on and off is good practice for Australian workplaces, coming as another major retail group revealed it underpaid workers by more than $61 million.

The Shop, Distributive and Allied Employees Association slammed Super Retail Group, which owns major brands Supercheap Auto and Rebel, for underpaying workers, a bill to revealed to be about $8 million more than previously announced.