The body tasked with oversight of the IRS announced in a letter that it will investigate the agency's use of location data harvested from ordinary apps installed on peoples' phones, according to a copy of the letter obtained by Motherboard.

The move comes after Senators Ron Wyden and Elizabeth Warren demanded a formal investigation into how the IRS used the location data to track Americans without a warrant.

"We are going to conduct a review of this matter, and we are in the process of contacting the CI [Criminal Investigation] division about this review," the letter, signed by J. Russell George, the Inspector General, and addressed to the Senators, reads. CI has a broad mandate to investigate abusive tax schemes, bankruptcy fraud, identity theft, and many more similar crimes. Wyden's office provided Motherboard with a copy of the letter on Tuesday.