The same Homeland Security Department office that categorized veterans as potential terrorists issued an earlier report that defined dozens of "extremists" ranging from black power activists to abortion foes. The report was nixed within hours and recalled from state and local law enforcement officials.
Here is one definition of interest:
(U) tax resistance movement (U//FOUO) Groups or individuals who vehemently believe taxes violate their constitutional rights. Among their beliefs are that wages are not income, that paying income taxes is voluntary, and that the 16th Amendment to the U.S. Constitution, which allowed Congress to levy taxes on income, was not properly ratified. Members have been known to advocate or engage in criminal activity and plot acts of violence and terrorism in an attempt to advance their extremist goals. They often target government entities such as the Internal Revenue Service and the Bureau of Alcohol, Tobacco, Firearms and Explosives. (also: tax protest movement, tax freedom movement, antitax movement)