The CTIA, an organization representing mobile phone operators, after the city passed an ordinance requiring retailers to hang posters noting that cellphones emit radio frequency energy. The posters also would offer tips for avoiding health risks possibly associated with such RF energy. In addition to the posters, the ordinance required retailers to place stickers with the warning on store displays and provide customers with fact sheets about limiting exposure to RF.

Judge William Alsup, who is presiding over the case in the U.S. District Court for the Northern District of California, found that requiring retailers to hang the poster "is not reasonably necessary and would unduly intrude on the retailers' wall space."

He also said that the sticker requirement is unconstitutional because it will "unduly intrude upon the retailers' own message."

He did, however, allow the requirement that retailers give each customer a fact sheet developed by the city, as long as the city accepts a few of his edits. While each of the facts on the sheet is accurate, the overall message is misleading, he wrote. "The overall impression left is that cell phones are dangerous and that they have somehow escaped the regulatory process. That impression is untrue," he wrote.

The ordinance says that retailers must give the fact sheet to everyone who buys a phone and to any other shoppers who request the fact sheet. Retailers will be fined for failing to comply.