
401(k) glossary
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Testing & compliance
Prohibited transaction
Short definition
A prohibited transaction is a dealing between a retirement plan and a party in interest, such as the employer, a fiduciary or a service provider, that ERISA and the tax code ban unless an exemption applies.
What a prohibited transaction is
The law bars sales, leases and loans between the plan and a party in interest, the use of plan assets for a party in interest’s benefit, and any act in which a fiduciary deals with plan assets in their own interest. Exemptions allow ordinary plan business, including participant loans and paying a service provider reasonable compensation for necessary services.
Why it matters to employers
In small plans the most common prohibited transaction is depositing employee deferrals late, which is treated as a loan from the plan to the employer. The tax is 15% of the amount involved for each year, reported on IRS Form 5330, and rises to 100% if the transaction is not corrected. Fiduciaries can also be personally liable for losses. The Department of Labor’s Voluntary Fiduciary Correction Program gives a path to fix many of these.
Example
An employer holds $20,000 of deferrals for 45 days longer than allowed. The amount involved is the interest on $20,000 for the late period, not the $20,000. The employer deposits the lost earnings and pays the 15% excise tax on the amount involved.
Common mistakes
Using plan assets to pay for expenses that belong to the employer, such as the cost of designing the plan.
Hiring a business owned by a fiduciary or a relative without checking for an exemption.
Having the plan buy or lease property from the owner.
Ignoring small late deposits.
Sources
Internal Revenue Service: Retirement topics: Prohibited transactions (https://www.irs.gov/retirement-plans/plan-participant-employee/retirement-topics-prohibited-transactions), retrieved 2026-11-11 U.S. Code (govinfo.gov): 29 U.S.C. 1106: Prohibited transactions (https://www.govinfo.gov/content/pkg/USCODE-2023-title29/html/USCODE-2023-title29-chap18-subchapI-subtitleB-part4-sec1106.htm), retrieved 2026-11-11 U.S. Code (govinfo.gov): 26 U.S.C. 4975: Tax on prohibited transactions (https://www.govinfo.gov/content/pkg/USCODE-2023-title26/html/USCODE-2023-title26-subtitleD-chap43-sec4975.htm), retrieved 2026-11-11 U.S. Department of Labor, EBSA: Voluntary Fiduciary Correction Program (https://www.dol.gov/agencies/ebsa/employers-and-advisers/plan-administration-and-compliance/correction-programs/vfcp), retrieved 2026-11-11
General information, not legal or tax advice.

