Both supermarkets will face the Federal Court on Wednesday accused of violating consumer law by the Australian Competition and Consumer Commission which says they misled shoppers on hundreds of popular supermarket items with their "Down Down" and "Prices Dropped" campaigns.
The alleged fake discounts included dairy, pet food, personal care, coffee, medicine, lollies, cereal and household cleaning products.
Woolworths said its Prices Dropped program was introduced to give "great everyday value". (Con Chronis/AAP PHOTOS)
The ACCC began separate proceedings against Woolworths Group Ltd and Coles Supermarkets Australia Pty Ltd in September.
At the time ACCC chair Gina Cass-Gottlieb alleged both supermarkets used similar ploys to increase prices of hundreds of products before dropping them as part of their respective campaigns.
The products sold for less than the inflated prices, but still more than the regular price that applied before the price spike.
The ACCC said, if successful, it would seek a significant penalty for the alleged breaches of consumer law.
Coles said it would defend the court proceedings, while Woolworths said its Prices Dropped program was introduced to give shoppers "great everyday value" on products.