Around 11,000 jobs could be axed because of cross-border spending sprees, Irish business chiefs have claimed.
Retail Ireland said every 150 shopping trips to the North resulted in one more person on the dole queue.
Figures from the Central Statistics Office (CSO) revealed southern customers spent €435m in Northern Ireland in a year.
Read Jamie Delargy's blog: Cross-border shopping
Shoppers forked out an average of €286 on their most recent trip, with the vast majority stocking up on groceries and almost half of them buying alcohol.
Retail Ireland director Torlach Denihan said the new figures from April to June 2009 highlighted the need for immediate action.
"The retail staff that will lose their jobs during 2009 earn over €400m," he said.
"The total cost to the State in income tax lost and social welfare payments for the 2009 job losses will be €220m."
Mr Denihan called on the Irish Government to reduce VAT to 18% to boost sales, and to reduce employers' PRSI to help the retail sector.
Paddy Malone from Dundalk Chamber of Commerce said the border town had lost around 1,000 retail jobs in the past 12 months.
"People are going North in their droves and the only real reason for going North is booze," he said.
"It's very hard for anybody in the drinks trade to survive, largely it's impossible.
"With the price difference, particularly of spirits North and South, there's no way to ask people to do their patriotic duty, people will vote with their pockets."
Peter Murray, manager of Newry's Buttercrane shopping centre, said he believed the figures for cross-border shopping had grown since the survey was compiled.
"Sales for this October were up 14% on last year. If that's reflective then you would imagine the next set of annual figures are going to be higher," he said.
Irish consumers have been urged to buy Irish products this Christmas.
© Press Association