Northern Ireland's First Minister has described the increase in cross-border shopping as the latest example of swings and roundabouts.
Peter Robinson said there were occasions in the past when it worked in the other direction.
Many Northern Ireland businesses are benefiting from the large increase in customers from the Republic.
Traders in towns such as Newry, Enniskillen and Derry have said 40% of their turnover comes from shoppers from the Republic.
The situation has led traders and politicians in the Republic to call on shoppers to be patriotic and shop at home.
But Mr Robinson said: 'There have been many occasions when it has worked in the other direction - it worked in terms of fuel aggregates when very clearly it damaged the prospects of businesses on our side of the border.
'I encourage people to come to Northern Ireland delighted that they built all those good roads so that people could come up quickly to Northern Ireland,' he added.
Deputy First Minister Martin McGuiness also gave his views, saying:
'We all know that human nature clearly tells us that over the course of many years people in the border areas, and indeed people wider afield, will travel almost anywhere to get a good bargain.'
