A city ordinance requiring cellphone retailers to provide a warning to customers about radiation exposure faces a legal battle less than a month after its passage.

CTIA ­– The Wireless Association, a nonprofit organization representing the wireless communications industry, has filed a lawsuit against the city of Berkeley, stating the ordinance violates CTIA members’ First Amendment rights. According to CTIA, many global health groups — such as the World Health Organization, or WHO — have not concluded that cellphone radiofrequency poses a health risk to consumers.

“It is unconstitutional to force cellphone retailers to communicate false, misleading and inflammatory information about their products,” said Theodore Olson, an attorney representing CTIA, in a statement.

Berkeley City Council passed the ordinance in May after working on it since 2011. Consulting with Lawrence Lessig, director of the Edmond J. Safra Center for Ethics at Harvard University, the city drafted the ordinance so that it would avoid the fate of a similar “right to know” ordinance in San Francisco, which was withdrawn by the city’s Board of Supervisors in 2013.

According to Joel Moskowitz, director of UC Berkeley’s Center for Family and Community Health, Lessig helped draft the ordinance in a way that sticks closely to the language that cellphone manufacturers use in their consumer disclosure statements.

“The language (is) basically from the manufacturers themselves,” said Councilmember Max Anderson, who spearheaded the ordinance. “So they should be suing themselves.”

But CTIA argues in its formal complaint that the language of the Berkeley ordinance is still “misleading” and “alarmist,” citing the Federal Communications Commission’s online statement that there “is no scientific evidence that proves that wireless phone usage can lead to cancer or a variety of other problems.”

Both the federal government and the WHO, however, are continuing to look into the possible health effects of radiofrequency exposure, which is why many supporters of the Berkeley ordinance believe a retailer-provided notice benefits consumers.

“(The notice) just says, to assure safety, the federal government requires that cellphones meet radiofrequency exposure guidelines,” Moskowitz said. “That’s not debatable.”

As of Monday, the city had not yet been served with legal papers, according to Berkeleyside. But Anderson said he is sure they will be coming soon, and when they do, Lessig — who had expected the ordinance to be challenged by cellphone manufacturers — will assist the city in its fight to maintain the ordinance.

“(Lessig) agreed to assemble a team of lawyers from Harvard Law to pro bono defend this ordinance,” Anderson said. “We will continue to implement this ordinance unless legally blocked by the courts.”

The ordinance is set to go into effect June 25.