A report from the Associated Press has suggested that Google records the locations of its users even after they have asked it not to.
This could impact up to 2 billion Android and Apple devices which use Google for maps or search. The study, verified by researchers at Princeton University, has angered US law-makers.
In response, Google has claimed that it gives users clear descriptions of its tools and how to switch them off.
The study discovered that users' locations are recorded even after location history has been disabled. For instance, Google stores a snapshot of your location when you open the maps app; automatic weather apps on Android phones roughly identify the whereabouts of a user; searches unrelated to location pinpoint the precise longitude and latitude of users.
To illustrate the effect of these location markers, AP made a visual map displaying the movements of Princeton researcher Gunes Acar whilst using an Android phone with the location history switched off.
The map displayed his train commute around New York alongside visits to The High Line park, Chelsea Market, Hell's Kitchen, Central Park and Harlem. It also showed his Home address.
To prevent Google from saving these location markers, users must turn off another setting named Web and App Activity, which is enabled by default and fails to mention location data.
Disabling this stops Google from storing information generated by searches and other activities that can restrict the effectiveness of its digital assistant.
On his blog, security researcher Graham Cluley writes 'You would think that telling Google that you didn't want your location to be tracked by disabling an option called "Location History" would stop the internet giant from storing data about your location. It seems pretty sneaky to me that Google continues to store location data, unless you both disable "Location history" and "Web & App Activity."'
Google said in response that 'There are a number of different ways that Google may use location to improve people's experience, including: Location History, Web and App Activity, and through device-level Location Services. We provide clear descriptions of these tools, and robust controls so people can turn them on or off, and delete their histories at any time.'
After its research, AP created a guide to show users how to delete location data.
After being shown the evidence collected during the AP study, Democratic senator Mark Warner accused technology companies of having 'corporate practices that diverge wildly from the totally reasonable expectation of their users'.
Republican senator Frank Pallone requested 'comprehensive consumer privacy and data security legislation'.
In Britain, a spokesman for the Information Commissioner's Office said to the BBC that 'Under the GDPR and the Data Protection Act 2018, organisations have a legal duty to be open, transparent and fair with the public about how their personal data is used. Anybody who has concerns about how an organisation is handling their personal information can contact the ICO.'
Currently, technology firms are being criticised for not being clear about privacy settings and how to use them. In June, a report from the Norwegian Consumer Council uncovered evidence that privacy-friendly options are hidden away or obscured.
Location-based advertising provides marketers with big opportunities. The BBC suggest that according to research firm BIA/Kelsey, in 2018 US brands are set to spend up to $20.6bn (£16.3bn) on targeted mobile ads.