Retailers that fail to display prices in a "clear and unambiguous manner" could face heavy fines under a crackdown on over-charging announced by the Tánaiste last night.
New regulations, to be introduced by Christmas, will also oblige shops to display the cost- per- unit of goods sold by quantity, Ms Harney told the annual conference of the Consumers' Association of Ireland.
The regulations would be "rigorously enforced", the Tánaiste said.
But she ruled out price control as a means of reining-in inflation, insisting competition was the best way of keeping prices in check.
Ms Harney urged the consumers' association to strengthen its ties with sister organisations across Europe, where the consumer lobby was much stronger.
She said: "Consumers in Ireland are not as organised as in other members states of the EU. As a consequence they do not have the same impact as other interest groups in informing policy process. I want to see this situation change."
Ms Harney insisted she was "implacably" opposed to price control, describing it as a discredited and ineffective instrument".
She said: "In the days of price control, maximum prices very quickly became minimum prices, the letter from the minister authorising an increase became the only price determinant.
"Competition took a back seat, inflation ran at more than 20 percent and consumers lost out."
A Dunnes Stores outlet in Limerick has been convicted for breaching consumer protection legislation. The store, at Sarsfield Street, was fined €600 for displaying rashers at an incorrect price.
The Director of Consumer Affairs welcomed the conviction.