Business is bracing for an unprecedented rise in the cost of weekend work if Bill Shorten is elected, as wages are expected to rise by up to 21 per cent after July 1, if Labor proceeds with its promise to increase penalty rates.

New analysis from the Australian Retailers Association shows Labor’s pledge to reverse cuts to Sunday penalty rates within the first 100 days would mean employers would suffer a triple wage hit when combined with minimum wage increases and further rises in award rates for evenings and Saturdays in the retail industry.