The Supreme Court on Friday said the government generally needs a warrant if it wants to track an individual's location through cell phone records over an extended period of time.
The ruling is a major victory for advocates of increased privacy rights who argued more protections were needed when it comes to the government obtaining information from a third party such as a cell phone company.
The 5-4 opinion was written by Chief Justice John Roberts siding with the four most liberal justices.
It is a loss for the Justice Department, which had argued that an individual has diminished privacy rights when it comes to information that has been voluntarily shared with someone else.
The opinion, which was limited to cell site location data, continues a recent trend at the court to boost privacy rights in the digital era and clarifies court precedent as it applies to data held by a third party.