26 CFR 301.7606-1: -1 Entry of premises for examination of taxable objects.

Any officer or employee of the Internal Revenue Service may, in the performance of his duty, 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 and also enter at night any such building or place, while open, for a similar purpose.