The ordinance, passed last year, would require the Sar figure to be displayed next to each phone being offered for sale, but has faced fierce opposition from within the industry, with a lawsuit from the industry trade body, the CTIA.

Although the ordinance remains on the statute books, the implementation date has now been postponed indefinitely.

The main challenge to the plans comes from the fact that the SAR figure, although widely used, is not that useful in determining how much radiation a phone emits as it is based on theoretical peak levels rather than the average that a user might experience.

Users buying smartphones with lower SAR ratings could find themselves exposed to higher levels of radiation depending on how they use the phone than had they brought a specially higher SAR rated phone.

It is expected that retailers may be required to have out non-specific advice about limiting usage as a compromise measure.