"The Internal Revenue Service functions as an intelligence agency in two respects. First, through its Intelligence Division, it both collects general intelligence about possible tax violators and investigates specific allegations of tax fraud to secure evidence for criminal prosecution. Second, the IRS accumulates vast amounts of information about the financial and personal affairs of American citizens from the tax returns and supporting information which Americans voluntarily submit each year. This report is primarily an exploration of the reasons these uses of the IRS have led to serious and illegal abuse of IRS investigative powers and to a compromise of the privacy and integrity of the tax return. As a rich deposit of intelligence and an effective intelligence gatherer, the IRS is a powerful tool which other agencies of government, including Congress and the executive branch, have periodically sought to employ for purposes other than tax law enforcement."
Supplementary Detailed Staff Reports on Intelligence Activities and the Rights of Americans - Book III (1976)