SAN FRANCISCO--Six of the world's top consumer technology firms have agreed to provide greater privacy disclosures before users download applications in order to protect the personal data of millions of consumers, California's attorney general said on Wednesday.

The agreement binds 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, 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.

Harris was also among U.S. state lawmakers who on Wednesday signed a letter to Google CEO Larry Page to express "serious concerns" over the web giant's recent decision to consolidate its privacy policy. The policy change would give Google access to user information across its products, such as GMail and Google Plus, without the proper ability for consumers to opt out, said the 36 U.S. attorneys general in their letter.

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."