26 U.S. Code § 533 - Evidence of purpose to avoid income tax
(a) Unreasonable accumulation determinative of purpose
For purposes of section 532, the fact that the earnings and profits of a corporation are permitted to accumulate beyond the reasonable needs of the business shall be determinative of the purpose to avoid the income tax with respect to shareholders, unless the corporation by the preponderance of the evidence shall prove to the contrary.
Source(Aug. 16, 1954, ch. 736, 68A Stat. 179.)