A Facebook post showing a bottle of Bella Cucina Prosecco sold in Tesco at £5.50 in Scotland and €17.99 in the Republic of Ireland has been shared thousands of times by angry shoppers.
The picture was posted on Friday by Irish student nurse Lisa Kiernan, who lives in Edinburgh and spotted the price difference when she returned home to Maynooth in Ireland last month.
She told BuzzFeed News she had not expected the post, which has now been liked 12,000 times and shared more than 5,600 times, to go viral, but had noticed the steep price difference because as a student she had to "watch my pennies".
Tesco told BuzzFeed News the prosecco was more expensive in the Republic of Ireland compared to the UK because alcohol in Ireland is subject to excise duty of €6.37 and 23% VAT, higher than the UK rate of 20%.
However, a spokeswoman said the supermarket has now reduced the drink to €14 on special offer and has other bottles at lower prices.
She also said it cost more for the company in freight costs to transport the product to Ireland, but did not confirm the price in Northern Ireland, which is part of the UK and therefore not subject to the higher rates.
Kiernan's Facebook post has racked up more than 1,000 comments since Friday. Some people shared pictures of cheaper prosecco at rival supermarkets, and others accused Tesco of ripping customers off.
Some even claim to have calculated it would be cheaper to fly Ryanair to Scotland and buy three bottles of the same drink there than it would be to buy three bottles at Tesco in Ireland.
However, it was not all fury. One user said: "Taxes in Ireland not retailers fault. Businesses are hit with huge overheads and taxes... Don't blame retailers look at the system."
Tesco added in a statement: "We work hard to offer our customers clear, fair and transparent pricing. ... Our local wine buying team based in Dublin regularly review our range and offers and the size of our product range means that customers can easily make a choice in store amongst the different products and brands available.
"We have also invested in reducing the price of hundreds of everyday products that matter most to our customers."