The Consumers' Association has accused retailers of driving shoppers north of the border by charging exorbitant prices for their products.
The association was responding to reports that thousands of pre-Christmas shoppers from the Republic are flocking to the North to avail of cheaper prices for alcohol, toys and other goods.
The favourable exchange rate between sterling and the euro is believed to be encouraging much of the exodus, but Michael Kilcoyne of the Consumers' Association said several chain stores with outlets on both sides of the border are also charging significantly more in the Republic.
"What it's doing is it's losing money for the economy of the south," he said.