Technology firms, including Apple and Google, have agreed to provide greater privacy disclosures before users download applications.
The agreement binds the six firms - Amazon, Apple, Google, Microsoft, Research In Motion, and Hewlett-Packard - and developers on their platforms - to disclose how they use private data before an app may be downloaded, California’s Attorney General Kamala D. Harris said.
"Your personal privacy should not be the cost of using mobile apps, but all too often it is," said Harris.
Currently 22 of the 30 most downloaded apps do not have privacy notices, said Harris. Some downloaded apps also download a consumer's contact book.
Google said in a statement that under the California agreement, Android users will have "even more ways to make informed decisions when it comes to their privacy".
Apple confirmed the agreement but did not elaborate.
EU authorities have asked Google to halt the policy change until regulators can investigate the matter.
California's 2004 Online Privacy Protection Act requires privacy disclosures, but Harris said few mobile developers had paid attention to the law in recent years because of confusion over whether it applied to mobile apps.
"Most mobile apps make no effort to inform users about how personal information is used," Harris said at a press conference in San Francisco. "The consumer should be informed of what they are giving up".
The six companies will meet the attorney general in six months to assess compliance among their developers. But Harris acknowledged "there is no clear timeline" to begin enforcement.
The attorney general repeatedly raised the possibility of litigation at some future time under California's unfair competition and false advertising laws if developers continue to publish apps without privacy notices.
"We can sue and we will sue," she said, adding that she hoped the industry would act "in good faith."
There are nearly 600,000 applications for sale in the Apple App Store and 400,000 for sale in Google's Android Market, and consumers have downloaded more than 35 billion, said Harris.
There are also more than 50,000 individual developers who have created the mobile apps currently available for download on the leading platforms, she said.
These figures are expected to grow. She said an estimated 98 billion mobile applications will be downloaded by 2015, and the $6.8 billion market for mobile applications is expected to grow to $25 billion within four years.