Privacy groups have asked the U.S. FCC to declare that even “anonymized” phone records have to be protected under a privacy rule that restricts carriers from sharing customers’ information without their consent.

The petition filed before the Federal Communications Commission comes in the wake of reports that U.S. carriers like Verizon and AT&T were sharing phone records in bulk with the U.S. government.

The groups cite research to state that even so-called anonymized call records have sufficient information to link back to specific individuals. “When a carrier purges individual identities from a set of call records but leaves individual characteristics (such as incoming and outgoing calls, call times, and call durations) intact, the records are not anonymous at all; they are pseudonymous,” according to their petition filed Wednesday before the FCC.

“We don’t know whether or not they actually are selling [customer proprietary network information], but the fact that they think they can is alarming.”

Section 222 of the Communications Act instructs carriers that, with few exceptions, they have to get customers’ consent before they can share “customer proprietary network information,” also referred to as CPNI, wrote Laura Moy, staff attorney at Public Knowledge, one of the groups filing the petition, in a blog post.

The groups found that all four major mobile carriers - AT&T, Sprint, T-Mobile, and Verizon - have privacy policies that suggest that they consider it okay to sell or share the records. “We don’t know whether or not they actually are selling CPNI, but the fact that they think they can is alarming,” Moy wrote.

The petition points out that in 2000, Latanya Sweeney, appointed last month chief technologist of the U.S. Federal Trade Commission, found during experiments she conducted that 87 percent of the U.S. population “had reported characteristics that likely made them unique based only on 5-digit ZIP, gender, date of birth.” Researchers from the University of Texas at Austin also found that “removing identifying information is not sufficient for anonymity,” the groups said.

The groups have asked the FCC to issue a declaratory ruling that non-aggregate call records, purged of personal identifiers but with customers’ individual characteristics intact, are protected as “individually identifiable CPNI,” and phone carriers including Verizon, AT&T, Sprint and T-Mobile must not sell the records without customers’ consent. The next step is for the FCC “to docket the petition and put it out on public notice for people to comment on it,” Moy said.

The National Security Agency on Wednesday claimed that bulk collection of phone records of U.S. residents was the best way available to track terrorists. Its director, General Keith Alexander, described the bulk collection to the U.S. Senate Judiciary Committee as the “least intrusive” way to track terrorist communications, and challenged critics to come up with a better way.