Cases related to 26 USC 7806:

Hall et al. vs. USA, 975 F.2d 722
Laing vs. US, 423 U.S. 161
U.S. vs. Reorganized CF, 518 U.S. 213
Juvenile Shoe Corporation vs. U.S.A., 99 F.3d 898
Motor Fuel Carriers, Inc. vs. U.S., 420 F.2d 702
Alcoa, Inc. vs. U.S.A., 509 F.3d 173
U.S. vs. Bisceglia, 420 U.S. 141
Natchez vs. U.S.A., 705 F.2d 671
Bank One Corporation vs. Commissioner of Internal Revenue, Docket 5759-95
Patton vs. U.S.A., 305 F.2d 655
Security State Bank vs. Commissioner of Internal Revenue, 214 F.3rd 1254
U.S.A. vs. Garland, 43 F.3d 1474
Nordby Supply company vs. U.S., 572 F2d 1377

Read the cases carefully. The gov't doesn't want the point to be really clear,
and they use subtle wording to avoid that clarity. Nevertheless, if you
understand the basic wording you can see that 26 USC is not law.