Under the Internal Revenue Code, separate legal entities can be treated as a single employer for benefit plan purposes when they share enough common ownership or operate in certain service relationships. The controlled group rules for employee benefit plans, set out in IRC Sections 414 and 1563, force those related businesses to combine their workforces when testing whether a retirement plan, health plan, or welfare plan meets federal qualification requirements. If your business is part of a controlled group, every employee across every member entity counts, whether or not the entity that employs them sponsors the plan.
Three structures trigger aggregation: parent-subsidiary groups, brother-sister groups, and combined groups. A fourth set of rules, the affiliated service group rules, reaches service businesses that would otherwise slip through the stock-ownership tests.
Parent-Subsidiary Controlled Groups
A parent-subsidiary controlled group exists when one entity owns at least 80 percent of the voting power or the total value of another entity’s stock.1Office of the Law Revision Counsel. 26 U.S. Code 1563 – Definitions and Special Rules The parent sits at the top, and the subsidiary or chain of subsidiaries extends downward.
The chain can extend through multiple tiers. If Company A owns 80 percent of Company B, and Company B owns 80 percent of Company C, all three form a single controlled group. Each link must independently meet the 80 percent threshold. Drop Company B’s stake in Company C to 79 percent and the link breaks; Company C falls out of the group.2eCFR. 26 CFR 1.1563-1 – Definition of Controlled Group of Corporations and Component Members and Related Concepts
These rules are not limited to corporations. The regulations extend the same principles to partnerships, sole proprietorships, trusts, and estates. For non-corporate entities, “controlling interest” means at least 80 percent ownership of the profits or capital interest in a partnership, or at least 80 percent of the actuarial interest in a trust or estate.3GovInfo. 26 CFR 1.414(c)-2 – Two or More Trades or Businesses Under Common Control
Brother-Sister Controlled Groups
A brother-sister group involves two or more organizations owned by the same small group of people rather than by a parent entity. The test looks at ownership by five or fewer individuals, estates, or trusts and requires two conditions to be met at the same time.2eCFR. 26 CFR 1.1563-1 – Definition of Controlled Group of Corporations and Component Members and Related Concepts
The 80 Percent Common Ownership Test
The same five or fewer owners must collectively hold at least 80 percent of the voting power or total value of each organization being tested. This looks at each entity independently: the ownership group must clear the 80 percent bar in Company X and separately clear it in Company Y. An owner’s full stake in each entity counts.
The More-Than-50 Percent Identical Ownership Test
The same group of owners must also hold more than 50 percent of each entity when counting only their identical ownership across all organizations. “Identical” means the smallest percentage a given owner holds in any of the entities. An owner with 60 percent of Company X and 20 percent of Company Y contributes only 20 percent to this test, because that is the level of ownership held identically in both.1Office of the Law Revision Counsel. 26 U.S. Code 1563 – Definitions and Special Rules
Both tests must pass. Failing either means the entities are not a brother-sister controlled group. The identical ownership test is the harder hurdle because it deliberately ignores lopsided ownership. Someone who owns 90 percent of one company and 5 percent of another contributes only 5 percent toward the 50 percent threshold.
Combined Groups
A combined group exists when three or more corporations are connected through both parent-subsidiary and brother-sister relationships. One corporation must be both the common parent of a parent-subsidiary group and a member of a brother-sister group.1Office of the Law Revision Counsel. 26 U.S. Code 1563 – Definitions and Special Rules All entities in the combined group are treated as a single employer.
Affiliated Service Groups
The affiliated service group rules exist because professionals found a straightforward way to game the stock-ownership tests. A medical practice, law firm, or consulting group could spin off its administrative staff into a separate entity with no common stock ownership, exclude those lower-paid employees from benefit plan testing, and pass nondiscrimination tests easily. Section 414(m) closes that gap by treating certain service organizations as a single employer regardless of whether they meet the stock ownership thresholds.4Office of the Law Revision Counsel. 26 U.S. Code 414 – Definitions and Special Rules
A “service organization” is one whose principal business is performing services rather than manufacturing products or selling goods. Three relationships trigger aggregation.
A-Organization Relationship
An A-organization is a service organization that is a shareholder or partner in a first service organization (the FSO) and either regularly performs services for the FSO or regularly works alongside the FSO in serving third-party clients. The ownership stake in the FSO can be any amount. A physician group holding even a small partnership interest in a hospital staffing entity, and regularly providing services through it, can create an A-organization relationship.
B-Organization Relationship
A B-organization performs a significant portion of its business for the FSO or an A-organization, and the services it provides are the type historically performed by employees in that service field. At least 10 percent of the B-organization’s ownership interests must also be held by people who are highly compensated employees of the FSO or an A-organization. A billing company owned partly by partners of a medical practice, handling most of the practice’s revenue-cycle work, is the classic example.
Management Function Organization
A separate category captures any organization whose principal business is performing management functions on a regular and continuing basis for another organization. The management entity and the organization it manages form an affiliated service group. This prevents an owner from housing all highly compensated managers in one entity and all rank-and-file workers in another.
How Attribution Rules Expand Ownership
Ownership percentages for controlled group purposes are not limited to stock or interests you hold directly. The constructive ownership rules under Section 1563(e) treat you as owning interests held by certain family members and business entities. They exist to prevent people from parking shares with relatives or through intermediary entities to stay below the 80 percent or 50 percent thresholds.
Family Attribution
Stock owned by your spouse is generally treated as yours, but there is an exception. Spousal attribution does not apply if all four of the following are true: you do not directly own any stock in the corporation, you are not a director or employee and do not participate in management, less than 50 percent of the corporation’s gross income comes from passive sources like rents, royalties, and dividends, and the stock is not subject to restrictions running in your favor or in favor of your minor children.1Office of the Law Revision Counsel. 26 U.S. Code 1563 – Definitions and Special Rules
Stock owned by your children under age 21 is attributed to you, and if you are under 21, your parents’ stock is attributed to you. Attribution from adult children, grandchildren, parents, and grandparents applies only if you already own more than 50 percent of the corporation’s voting power or value. Grandparent attribution does not automatically kick in for every family situation; it only expands attribution for individuals who already hold a controlling position.
Option Attribution
If you hold an exercisable option to buy stock, the IRS treats you as already owning those shares. That prevents someone from staying just under 80 percent by holding options instead of stock while still exercising practical control.5eCFR. 26 CFR 1.1563-3 – Rules for Determining Stock Ownership
Entity Attribution
Ownership held by partnerships, estates, and trusts flows proportionally to the partners or beneficiaries. If a partnership owns 100 percent of a corporation and you are a 50 percent partner, you are treated as owning 50 percent of that corporation. These rules can create controlled group relationships that are invisible on a corporate org chart but very real for plan compliance.
What Aggregation Actually Changes
Once entities are aggregated, the single-employer treatment reaches almost every compliance test that measures headcount, coverage, or benefits.
Retirement Plan Coverage and Nondiscrimination
Retirement plans like 401(k)s and defined benefit pensions must satisfy minimum coverage requirements to keep their tax-favored status. The coverage test measures whether the plan benefits enough rank-and-file employees relative to highly compensated employees, counting workers across the entire controlled group, not just the sponsoring entity.6eCFR. 26 CFR 1.410(b)-2 – Minimum Coverage Requirements (After 1993) An owner who runs two companies and offers a 401(k) through only one still has to count the other company’s employees.4Office of the Law Revision Counsel. 26 U.S. Code 414 – Definitions and Special Rules Nondiscrimination testing works the same way.
Section 415 Contribution Limits
All defined contribution plans maintained by any controlled group member are treated as a single plan when checking whether a participant’s total annual additions exceed the cap, and the same rule applies to defined benefit plans.7eCFR. 26 CFR 1.415(f)-1 – Aggregating Plans Sponsoring a 401(k) through one entity and a profit-sharing plan through another does not let an owner double up on contribution limits.
ACA Employer Mandate
The Affordable Care Act requires applicable large employers to offer affordable coverage to full-time employees. Whether an employer crosses the 50-full-time-equivalent threshold depends on the combined headcount of the entire controlled group. Two businesses with 30 employees each that share common ownership are collectively a 60-employee employer for ACA purposes, even if neither would be subject to the mandate on its own.
COBRA and HIPAA
Federal COBRA continuation coverage applies to employers with 20 or more employees, and the employee count aggregates across the controlled group. Two businesses with 12 employees each can be COBRA-covered employers if they share common ownership. Controlled group determinations also affect HIPAA portability and creditable coverage rules for group health plans.
Joint and Several Pension Liability
When a defined benefit pension plan terminates with insufficient assets, the plan sponsor and every member of its controlled group become jointly and severally liable to the Pension Benefit Guaranty Corporation for the unfunded benefit liabilities, plus interest.8Pension Benefit Guaranty Corporation. Response to Motion to Compel That shared liability extends to minimum funding contributions and PBGC premiums. A financially healthy company in a controlled group can be on the hook for pension debt that a struggling affiliate created.
Multiemployer pension plans create a parallel risk. When a contributing employer withdraws from a multiemployer plan, every entity under common control with the withdrawing employer shares joint and several liability for the withdrawal liability assessment.
Transition Relief After a Merger or Acquisition
When an acquisition or merger changes the composition of a controlled group, the new employees do not have to be folded into existing plan coverage testing immediately. Section 410(b)(6)(C) provides a transition period that begins on the date of the transaction and runs through the last day of the first plan year that starts after the transaction date.9Office of the Law Revision Counsel. 26 U.S. Code 410 – Minimum Participation Standards For a calendar-year plan, an acquisition that closes in March 2026 gives the sponsor until December 31, 2027, to bring coverage testing into compliance.
Two conditions must be met. The plan must have passed coverage testing immediately before the transaction; a plan already out of compliance cannot use the grace period to defer fixing the problem. And the plan’s coverage cannot change significantly during the transition period beyond what naturally results from the new group composition.
The transition period only relieves the testing obligation. It does not override the plan document. If a plan’s eligibility provisions automatically cover all employees of controlled group members, the newly acquired employees may be entitled to participate immediately regardless of the testing grace period. Review your plan document for automatic-inclusion language before an acquisition closes, and amend if needed.
What Happens If You Get It Wrong
Failing controlled group coverage or nondiscrimination testing can lead to plan disqualification, and the consequences hit from several directions.
Highly compensated employees are hit hardest. If a plan is disqualified solely because it fails coverage or nondiscrimination requirements, each highly compensated employee must include the full value of their vested account balance in income for the year of disqualification, to the extent those amounts have not already been taxed. Non-highly compensated employees are generally protected: they owe tax on employer contributions only when they actually receive distributions.10Internal Revenue Service. Tax Consequences of Plan Disqualification
Distributions from a disqualified plan cannot be rolled over to an IRA or another qualified plan. Contributions to the trust also become subject to Social Security, Medicare, and federal unemployment taxes.
The employer loses its ability to deduct contributions when they are made. The deduction is deferred until the contribution becomes taxable income to the employee. For a defined benefit plan that does not maintain separate accounts for each participant, the employer may lose the deduction entirely. The plan trust itself loses tax-exempt status and must begin filing income tax returns on its investment earnings.
The IRS does offer correction programs that can fix testing failures before they escalate to disqualification. The Employee Plans Compliance Resolution System allows plan sponsors to self-correct certain operational errors or submit voluntary correction applications for more complex problems. Catching and correcting a controlled group testing failure early is far less costly than a formal disqualification.