This has been discussed on these boards, but some conflicting opinions from elsewhere have made this. IRC §4975 does not apply to an ERISA 403(b) plan, but ERISA 3(2) includes 403(b) plans. That, in turn, makes an ERISA 403(b) plan subject to the prohibited transaction rules, but not under 4975, under ERISA 406. Does this cause an ERISA 403(b) plan to be subject to an excise tax that requires Form 5330, thus completing the section of the form under 4975 and paying the 15% excise tax?