California Attorney General Kamala Harris has given 100 mobile app makers 30 days to comply with the state's new privacy laws.
"Protecting the privacy of online consumers is a serious law enforcement matter," said Harris.
"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."
App developers who do not comply with California privacy laws could face a fine of up to $2,500 for each non-compliant app downloaded.
The move could have impact outside of the state and the US, as the modified applications would be made available worldwide.
Mobile data collection has become a growing issue over the past year. The Federal Trade Commission (FTC) recently laid out guidelines for developers to make sure they comply with US privacy law. European data regulators also recently called out Google for unlawful data collection earlier this year.
This also isn't the first time Harris has got involved with mobile data collection laws. The Attorney General worked with companies such as Google, Apple and Microsoft to bring app marketplaces in line with California privacy laws earlier this year.
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