The legislation would require cell phone retailers to post radiation levels next to each phone in a font at least as large as the price. The retailers also would have to inform customers about what the radiation levels mean.
Scientists do not agree on whether radiation from cell phones poses any health hazard.
The federal government has established limits for safe exposure. The Federal Communications Commission says all phones legally sold in the U.S. are safe.
Newsom spokesman Joe Arellano says a bill to enact the rules likely will go before the Board of Supervisors within the next few months.