The IRS is under investigation by the US Treasury’s Inspector General for purchasing smartphone data to illegally track Americans.

The issue began when Senators Ron Wyden and Elizabeth Warren sent a letter to the Inspector General demanding the IRS be investigated. According to the letter, the IRS had been purchasing bulk data from a company named Venntel. The information contained location data from Americans’ phones, based on the various apps they use.

According to Motherboard,a Wyden aide has said “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.”

As Wyden and Warren’s letter points out, the Supreme Court ruled in 2018 that collecting significant quantities of historical data from phones was covered under the Fourth Amendment, and therefore requires a search warrant. The fact that the IRS obtained no such warrant puts it in legally dubious territory.

Putting aside the legal ramifications, it’s a safe bet that few Americans would be OK with the IRS tracking where they sleep at night.