Treas. Reg. § 54.6011-1

(a) Minimum funding standards or excess contributions for self-employed individuals and section 403(b)(7)(A) custodial accounts. Any employer or individual liable for tax under section 4971, 4972 or 4973(a)(2) (for a custodial account under section 403(b)(7)(A)) shall file an annual return on Form 5330 and shall include therein the information required by such form and the instructions issued with respect thereto.

(b) Tax on prohibited transactions. Every disqualified person (as defined in section 4975(e)(2)) liable for the tax imposed under section 4975(a) with respect to a prohibited transaction shall file an annual return on Form 5330 and shall include therein the information required by such form and the instructions issued with respect thereto. The annual return on Form 5330 shall be filed with respect to each prohibited transaction and for each taxable year (or part thereof) of the disqualified person in the taxable period (as defined in section 4975(f)(2)) beginning on the date on which such prohibited transaction occurs.