Retailers who overcharge must be "named and shamed" by consumers, Fine Gael has said.
Using official Department of Finance figures, the party has found that consumers are paying 44 per cent more for home-heating oil than their Northern Ireland counterparts.
"They pay 43 per cent more for a long-necked bottled of beer, 36 per cent more for vodka, 23 per cent more for wine," said the party's deputy leader, Mr Richard Bruton.
"The only relief is cheaper motor fuel to get up North to do your shopping, and cheaper cigarettes, despite all the hype from Government about being anti-smoking," he declared.
Higher tax and excise in the Republic account for 75 per cent of the difference in the price of a bottle of wine on both sides of the Border and half the difference in beer.
"However, when you strip out the impact of tax, you find a consistent pattern of higher pre-tax prices in the South.
"Once again the figures confirm a pattern of much higher mark-ups," he said.
Pre-tax prices in the Republic are, on average, 14 per cent dearer than in Northern Ireland, the statistics given to Mr Bruton by the Department of Finance show.