Tánaiste Mary Harney has reminded shopkeepers that new laws on the display of prices come into effect tomorrow.
Under the regulations, retailers face fines of up to €3,000 if they fail to display a unit price for all packaged products sold by weight or volume.
The law applies in all retail outlets, from supermarkets to corner-shops to mail order firms, and even applies to produce sold on the internet.
Ms Harney has warned that the Director of Consumer Affairs will be monitoring the situation to ensure that the legislation is complied with.
The law was designed to make it easier for consumers to compare prices and shop around for the best value.