Any taxpayer who engages in any illegal activities as defined in Chapters 9, 10 and 10.5 of Title IX of Part 1 of the Penal Code shall be denied all deductions from gross income attributable to such activities. Illegal activities include, but are not limited to the following:
The same rule applies in respect of any deduction attributable to any other business activity which is connected or associated with, or tends to promote or further any illegal activities. Every business activity which is carried on by any taxpayer, or by another under its direction or control, on the same premises where the illegal activities are conducted, tends to promote or further such illegal activities.
The same rule further applies to every business activity carried on by any taxpayer or by another under its direction or control, on the premises other than where the illegal activities are conducted and which tends to promote or further such illegal activities.
On and after May 3, 1951, all deductions from gross income attributable to such illegal activities shall be denied.
Cal. Code Regs. Tit. 18, § 24436