26 U.S.C. § 7601

(a) General rule The Secretary shall, to the extent he deems it practicable, cause officers or employees of the Treasury Department to proceed, from time to time, through each internal revenue district and inquire after and concerning all persons therein who may be liable to pay any internal revenue tax, and all persons owning or having the care and management of any objects with respect to which any tax is imposed. (b) Penalties For penalties applicable to forcible obstruction or hindrance of Treasury officers or employees in the performance of their duties, see section 7212.