Sen. Al Franken (D-Minn.) asked the Justice Department on Thursday to explain its practices for gathering data on people's cellphone locations.
In a letter to Attorney General Eric Holder, Franken asked how often the Justice Department requests that wireless carriers turn over the location data of their customers and what legal standard the department believes should apply.
The Supreme Court ruled earlier this year in United States v. Jones that tracking a suspect's car using a GPS device qualifies as a search under the Fourth Amendment.
Franken said that police who obtain location records from wireless carriers might be "working around" the Supreme Court's decision.
"I was further concerned to learn that in many cases, these agencies appear to be obtaining precise records of individuals’ past and current movements from carriers without first obtaining a warrant for this information," Franken wrote. "I think that these actions may violate the spirit if not the letter of the Jones decision."
Franken asked Holder to explain how the Supreme Court's decision affects the gathering of cellphone data and whether the Justice Department's practices have changed since the ruling.
He requested that the Justice Department respond within one month.
"I believe that this is an urgent matter and one that will provide critical information for policymakers and privacy advocates alike," he wrote.
The ACLU applauded Franken in a blog post.
"Letters like these are the first step in oversight," wrote Chris Calabrese, an ACLU legislative counsel. "We can’t wait to hear the answers."