case@ (Recasts first paragraph, adds quotes from Justices Sotomayor, Roberts, Alito, Kennedy)
WASHINGTON, Nov 29 (Reuters) - U.S. Supreme Court justices signaled on Wednesday they may impose limits on the ability of police to obtain cellphone data from wireless providers to track the location of criminal suspects in a major test of privacy rights in the digital age.
During arguments in the closely watched case involving a convicted robber, several of the nine justices across the ideological spectrum indicated concern about the use of data revealing a suspect's past locations, based on the cellphone towers that relayed calls, without a court-issued warrant.
The court potentially could rule that such a practice by law enforcement authorities amounts to an unreasonable search and seizure under the U.S. Constitution's Fourth Amendment. A ruling is due by the end of June.
Such a ruling would have a significant effect on law enforcement authorities that routinely request and receive this data from wireless providers in thousands of criminal investigations annually as they try to link suspects to crimes.
Liberal Justice Sonia Sotomayor was the most direct in raising the alarm about the increasing amount of data that government agencies can potentially obtain, at one point noting that most Americans "want to avoid Big Brother," referring to the symbolic all-seeing leader in George Orwell's dystopian novel "1984."
The justices heard an extended 80-minute argument in an appeal brought by a man named Timothy Carpenter convicted in a series of armed robberies in Ohio and Michigan with the help of past cellphone location data that linked him to the crime scenes. His American Civil Liberties Union lawyers have argued that without a warrant such data amounts to a Fourth Amendment violation.
The legal fight has raised questions about the degree to which companies protect their customers' privacy rights. The big four wireless carriers, Verizon Communications Inc, AT&T Inc, T-Mobile US Inc and Sprint Corp, receive tens of thousands of these requests annually from law enforcement.
Although the case involves location information, Sotomayor raised broader questions about digital privacy, saying cellphone providers could potentially obtain information on "the most intimate details of your life."
There is a possibility the court's four liberal justices could form a majority with one or more of the five conservatives, potentially including Chief Justice John Roberts and the court's newest member, Neil Gorsuch.
Roberts mentioned a 2014 Supreme Court ruling that he authored that required police in most instances to obtain a warrant to search a cellphone's contents when its user is arrested. Roberts reiterated what he said then, that smartphones packed with data-rich applications are now ubiquitous. He also said people have little power over the constant stream of information.
But conservative Justice Samuel Alito appeared concerned about setting new limits on the government's ability to obtain certain business records that authorities currently can get without a warrant, including data on financial transactions.
Alito questioned whether location information is more sensitive than bank records, a sentiment that fellow conservative Justice Anthony Kennedy appeared to share.
The justices seemed to differ on what they think Americans know about the prevalence of cellphone data. Sotomayor said Americans do not know the extent of it, while the 81-year-old Kennedy said even he knows how much data that carriers have on customers. "If I know it, everybody does," Kennedy said.
Police helped establish that Carpenter was near the scene of the robberies of Radio Shack and T-Mobile stores by securing from his cellphone carrier his past "cell site location information," which tracks which cellphone towers relay calls.
There is increasing scrutiny of the surveillance practices of U.S. law enforcement and intelligence agencies amid civil liberties concerns among lawmakers across the political spectrum.
The Supreme Court twice in recent years has ruled on major cases concerning how criminal law applies to new technology, both times ruling against law enforcement, including the 2014 case Roberts mentioned. In 2012, the court also decided that a warrant is needed to place a GPS tracking device on a vehicle.
The ACLU has said police need "probable cause," and therefore a warrant, in order to avoid a Fourth Amendment violation. But the U.S. Justice Department said probable cause should not be needed to obtain customer records under a 1986 federal law called the Stored Communications Act.
The Justice Department said prosecutors must show only that there are "reasonable grounds" for records that are "relevant and material" to an investigation to be provided.
Carpenter's bid to suppress the evidence failed and he was convicted of six robbery counts. On appeal, the Cincinnati-based 6th U.S. Circuit Court of Appeals upheld his convictions, finding that no warrant was required for the cellphone data.
(Reporting by Lawrence Hurley; Editing by Will Dunham)