A two-day hearing in Christchurch District Court began on Monday and will continue into Tuesday.
Police alcohol harm prevention officer, Inspector Ian Paulin, has applied to the Alcohol Regulatory and Licensing Authority to suspend the off-licences of 35 Foodstuffs South Island's New World supermarkets - the majority of stores in the South Island.
The Sale and Supply of Alcohol Act only allows discounts of more than 25 percent to be promoted inside licensed premises.
Paulin alleged the supermarket chain had breached those rules through online advertising relating to the advertisement of DB Export Beer which was advertised with a discount of 26.1 percent.
Paulin said the situation was not isolated to one store.
Ashburton New World owner Jeremy Rooney was cross examined on Monday morning.
He was asked by the prosecution why he did not know that the advertisement was not legal.
"There are 18,000 products in my store, to know the price of all of them is not possible."
Rooney told the court the supermarkets received the planned sales about four weeks ahead of them going live, but it did not show the discount percentage, only the cost price, sale price and GDP.
The hearing continues.
