http://www.subguns.com/laws/iif1.htm
In addition, if one is also a SOT, ATF claims to have the
right to enter onto your business premises, during business
hours, to verify compliance with the NFA. Their regulation to
that effect is found at 27 CFR sec. 179.22. The regulation is
apparently based upon 26 USC sec. 7606:
7606. Entry of premises for examination of taxable
objects.
(a) Entry during day.
The Secretary may enter, in the daytime, any building
or place where any articles or objects subject to tax are
made, produced, or kept, so far as it may be necessary for
the purpose of examining said articles or objects.
(b) Entry at night.
When such premises are open at night, the Secretary may
enter them while so open, in the performance of his official
duties.
(c) Penalties
For penalty for refusal to permit entry or examination, see
section 7342.
As 26 USC sec. 7342 provides for the penalty for a refusal to
permit entry under section 7606 it is worth a look:
7342. Penalty for refusal to permit entry or examination.
Any owner of any building or place, or person having the
agency or superintendence of the same, who refuses to admit
any officer or employee of the Treasury Department acting
under the authority of section 7606 (relating to entry of
premises for examination of taxable articles) or refuses to
permit him to examine such article or articles, shall, for
every such refusal, forfeit $500.
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it looks like the NFA corporation dispute was because of a misunderstanding. Robert was referring to a corporation that is a class III dealer, who would be subject to such searches as a dealer. However, it looks like chet was referring to a corporation that merely was an NFA weapon owner, and not a dealer. In that case, the corporation still has the same 4th ammendment rights as any individual.