The rule-making Committee of Advertising Practice is warning retailers that they must stop exaggerating price claims and making unfair comparisons.
Failure to do so will not only provoke anger among customers but action by the Advertising Standards Authority, the committee warns.
The move comes in the wake of increasingly aggressive price wars by supermarkets, telecoms companies and electrical suppliers.
Andrew Brown, the CAP chairman, said: "It's become a very tense area."
The new guidelines come in the week the ASA upheld complaints by Homebase against a national press campaign by its B&Q rival. The ad was headed: "Homebase lowered their higher prices on these products to compare them to ours. Next thing they did was to put them up again."
The new CAP rules require advertisers to identify when and where comparative surveys were carried out. It also says that price comparisons should be made only with retailers in the same locality unless it can be shown that it makes no difference to compare prices with retailers in other areas.
Nor must companies exaggerate the length of time for which their prices have been lower than their competitors, and they must ensure that the selection of goods chosen constitutes a fair comparison.