The Supreme Court agreed Monday to decide its biggest privacy dispute in years, a case that asks whether the authorities need a probable-cause court warrant to access people’s mobile phone location history.

“Because cell phone location records can reveal countless private details of our lives, police should only be able to access them by getting a warrant based on probable cause,” said Nathan Freed Wessler, a staff attorney with the American Civil Liberties Union. “The time has come for the Supreme Court to make clear that the longstanding protections of the Fourth Amendment apply with undiminished force to these kinds of sensitive digital records.”

For years, the authorities have been obtaining data pinpointing the cell towers that a suspect’s mobile phone pinged—all without a warrant. That information is then used as evidence showing a suspect’s past whereabouts. In the case before the justices, the authorities got 127 days of cell-site information that included 12,898 location points as part of a Detroit robbery investigation.