California attorney general sends privacy warnings to app makers

In a statement, United argued that it already has a privacy policy available on its website.

"We are committed to protecting our customers' data and personally identifiable information," the company said. "We are taking all steps necessary and appropriate to ensure compliance with California law as it relates to our mobile app."

Delta acknowledged it received the letter and said it intends to "provide the requested information."

Open Table did not immediately respond to a request to comment

The California Online Privacy Protection Act requires online services that collect personal information from Californians to conspicuously post a privacy policy. Companies can face a $2,500 fine for every violation of the law.

Harris argues that the law also covers mobile apps. She reached a deal in February with Apple, Google, Microsoft and other major companies to voluntarily post privacy policies for mobile apps. Facebook agreed to the app privacy requirements in June.

“Protecting the privacy of online consumers is a serious law enforcement matter,” Harris said in a statement. “We have worked hard to ensure that app developers are aware of their legal obligations to respect the privacy of Californians, but it is critical that we take all necessary steps to enforce California’s privacy laws.”

—Updated at 7:24 p.m.