Magistrate Judge James Orenstein of the Eastern District of New York issued an order on Monday denying the Justice Departments application for disclosure of information regarding wireless subscribers.
The Department of Justice had asked that carriers be required to provide information on individual subscribers, including details on caller location, outbound call origination and call termination, to help in its surveillance of potential suspects.
As part of the request, the Justice Department also asked for clearance to seek such customer data in real time, as callers are using their phones.
If approved, the application would have allowed law enforcement officials to essentially use cell phones as tracking devices to observe where people are traveling and with whom they are speaking without first proving in court why it should be allowed to do so.
The New York ruling concurs with a similar decision handed down in a Texas District Court in September that blocked the same practice in that state. In both cases, the applications had been filed in regard to ongoing investigations being pursued by the Justice Department against specific individuals.
Both rulings dealt with requests to use cell phone data garnered via so-called Pen Registers and other tapping devices that can be used to gather phone call records, and cellular site access information that could give away a callers location.
"Existing law does not permit the government to obtain the requested information on a prospective, real-time basis without a showing of probable cause," Orenstein wrote.
"To obtain such disclosure, the government must offer specific facts showing that there are reasonable grounds to believe that ... the records or other information sought are relevant and material to an ongoing criminal investigation."
Department of Justice representatives didnt immediately return calls seeking comment on the ruling.
The judge indicated in his decision that the federal government may be able to get permission to garner such cell phone information without sufficient proof in extreme circumstances, with a courts approval, but said tracking should not be allowed in matters of routine investigation.
Beyond the specifics of the law, Orenstein said Congress has not addressed the issue specifically, but that existing laws do provide clear enough guidance.
"When the government seeks to turn a mobile telephone into a means for contemporaneously tracking the movements of its user, the delicately balanced compromise that Congress has forged between effective law enforcement and individual privacy requires a showing of probable cause," the judge wrote in his decision.
At least one privacy advocacy group cited the New York decision as a win for individual privacy rights, with the Electronic Frontier Foundation labeling the ruling as a "smack down" to the Justice Department.
As part of his ruling, Judge Orenstein cited a brief filed by the EFF, a San Francisco-based nonprofit organization, which had argued against the cell phone data requests.
According to Kevin Bankston, an attorney with the EFF, the Justice Department has routinely been granted access to wireless subscriber data without proving probable cause by courts that he said have misinterpreted the same laws cited by Orenstein in his denial.
"This is a great victory for personal privacy rights; our cell phones reveal an enormous amount about us and can reveal everywhere we go, who we associate with and even what we believe in many ways," Bankston said. "The government should need to get probable cause before being able to track that information."
"The broader issue is that we have a system that authorizes surveillance in secret, and the problem is that judges are given paperwork by the Department of Justice without sufficient briefing, and they sign them," he said. "The same can be said of the phone companies: If they get something signed by a judge, they tend to cooperate with asking questions."
As a result of the New York and Texas cases, Bankston said he believes that other judges will begin enforcing the law more conservatively and shunning future law enforcement requests.
He said that in an earlier brief filed with New York, the Justice Department detailed another form of previously unknown form of surveillance known as a "hot watch" wherein the government has been granted individual credit card wiretaps without providing probable cause.
"A lot of judges will realize just how much theyve been misled and I think well see more decisions like this, and well hear about even more surveillance powers the government has been able to pass off," Bankston said.
"The foreign intelligence arena is even more crowded in secrecy and ripe for abuse, and we should find out just what else theyve been getting away with."