"In June, officials from the IRS Criminal Investigation unit told Wyden's office that it had purchased location data from a contractor called Venntel, and that the IRS had tried to use it to identify individual criminal suspects. Venntel obtains location data from innocuous looking apps such as games, weather, or e-commerce apps, and then sells access to the data to government clients.

A Wyden aide previously told Motherboard that the IRS wanted to find phones, track where they were at night, use that as a proxy as to where the individual lived, and then use other data sources to try and identify the person. A person who used to work for Venntel previously told Motherboard that Venntel customers can use the tool to see which devices are in a particular house, for instance.

The IRS' attempts were not successful though, as the people the IRS was looking for weren't included in the particular Venntel data set, the aide added.

But the IRS still obtained this data without a warrant, and the legal justification for doing so remains unclear. The aide said that the IRS received verbal approval to use the data, but stopped responding to their office's inquiries.

The Inspector General specifically said they would investigate the legal argument used.

"You requested that TIGTA investigate CI's use of commercial databases in the performance of its duties, and that TIGTA examine the legal analysis IRS lawyers performed to authorize this practice. Your concern is that CI's use of the data described above may not be consistent with the holding of the Supreme Court in the case Carpenter v. United States," the Inspector General's letter continues, referring to the Treasury Inspector General for Tax Administration.

"Upon compilation, to the extent allowable under the law, we will advise you of the results," the letter adds.

The IRS did not immediately respond to a request for comment."