A federal appellate panel on Wednesday rejected a constitutional challenge to warrantless collection of cellphone location records, increasing the potential for the US supreme court to consider the legality of the practice.

In a 22-page opinion issued by the sixth circuit court of appeals, the judges said the FBI’s collection of records from wireless carriers for phone numbers connected to two Detroit men was constitutional.

Timothy Carpenter and Timothy Sanders, who were convicted for their role in a string of cellphone store robberies, argued the practice was a constitutional violation under the fourth amendment. A brief filed by the American Civil Liberties Union noted that the location tracking in this case reveals the “extraordinary private details” police can obtain via location tracking, including where the defendants may worship and who they may be sleeping with.

The appellate panel disagreed in the ruling, saying the pair had “no expectation of privacy” for location information. The judges added the records are unprotected, as they “say nothing about the content of any calls”.

In early 2011, law enforcement officials arrested four men suspected in a string of armed robberies around metro Detroit. One of the men confessed to multiple robberies and proceeded to cooperate with the FBI, handing over his phone number, as well as 16 others linked to other possible suspects. Investigators then sought orders to obtain records for “cell site information” for the phone numbers on incoming and outgoing calls over several months, the opinion said.

The judges granted the orders. The ACLU found investigators obtained records that included nearly 13,000 separate location points for Carpenter, and more than 23,000 for Sanders, which they calculated was an average of one every six minutes.

As a result, Carpenter and Sanders were charged with aiding and abetting multiple robberies. The pair’s motion to suppress the cell location data, contending that a warrant with probable cause was required to obtain the records, was denied by the lower court. The opinion said that Carpenter was described in court as the organizer of several robberies, where Sanders “had served as lookout”.

The court reasoned that the defendants do not have a reasonable expectation of privacy in “third-party” data such as that from a cellphone carrier. The judges also distinguished between the content of communications such as emails and location information.

”[T]he cell-site data – like mailing addresses, phone numbers, and IP addresses – are information that facilitate personal communications, rather than part of the content of those communications themselves,” the ruling stated.

ACLU attorney Nate Wessler disagreed.

“When we did our own analysis of this location records … we were able to tell things like when the defendant spent the night at home and spent the night at a different neighborhood,” Wessler said. “These records when they’re aggregated can be very sensitive and it’s very important that our understanding of the fourth amendment keeps pace with the advancing technology.”

Judge Jane Stranch joined the majority opinion but took issue with the “sheer quantity of sensitive information procured without a warrant,” which “raises fourth amendment concerns”. Stranch also said there was a need to develop a new test to determine when a warrant is needed to obtain similar records.

“The runaway pace of technological development makes this task more difficult,” she said. “But the job is ours nonetheless and the circumstances before us lead me to believe that we have more work to do to determine the best method.”

The ruling is consistent with separate regional appeals courts, but conflicts with an August ruling by the fourth circuit court of appeals, which found that: “Even as technology evolves, protections against government intrusion should remain consistent with those privacy expectations society deems reasonable.”

Wessler said he believes the conflicting opinions suggest “more courts certainly will be taking up this question at the appellate panel”.

“And perhaps the supreme court will have to weigh in eventually to set a consistent standard across the country,” he said.

The US attorney’s office in Detroit, which prosecuted the case, declined to comment.

Carpenter’s attorney, Harold Gurewitz, said his client may ask the sixth circuit to rehear the case or petition the supreme court for consideration.

“It concerns an issue that I think is important,” he said, “one that’s been raised in other courts across the country, both state and federal, so it is important and we’re going to look at it real quickly.” Gurewitz said the supreme court needs to step in to resolve the issue at some point.

“Technology has moved forward at a speed that has continued to increase,” he said. “And I think it’s time to give the [supreme] court an opportunity to talk about how the law ought to address these … issues.”

Sanders was already serving a 30-year sentence for murder, and received an additional 14 years for his role in two robberies. Carpenter was sentenced to over 116 years in prison, which the court also found to be legal.

“Carpenter has a long criminal history,” the opinion said. “In this case, as the district court observed, Carpenter organized and led several ‘very violent’ robberies that put his victims ‘in extreme danger’.”