What Is IRC 3121? Employment, Wages, and Exclusions

IRC 3121 is the section of the Internal Revenue Code that sets the ground rules for Federal Insurance Contributions Act (FICA) taxes. It does this by defining three terms — “employment,” “employee,” and “wages” — and then listing the specific exclusions that pull certain workers and payments back out.¹ For 2026, when those definitions are met, wages are taxed at 6.2% for Social Security (up to $184,500) and 1.45% for Medicare (no cap), with the employer and employee each paying their share.²

The Three Definitions That Trigger FICA

FICA does not apply to every payment a business makes to every person. It applies when a payment is “wages,” made to an “employee,” for “employment.” All three boxes have to be checked. IRC 3121 spends most of its length defining each term and then carving exclusions out of each one. Reading the statute in that order — employment, employee, wages — is the fastest way to understand why a given worker or payment is or isn’t covered.

When Work Counts as Employment

The statute defines “employment” as any service an employee performs for the person employing them. The citizenship or residency of either party is not the threshold question. Location is.¹

Services performed inside the United States are almost always employment, regardless of the worker’s nationality or length of stay. The definition also reaches services on American vessels or aircraft when the contract was entered into in the U.S., and services a U.S. citizen or resident performs overseas for an American employer.¹

Foreign Affiliates

Section 3121(l) lets an American parent company enter an agreement with the Treasury Department to extend FICA coverage to U.S. citizens and residents working abroad for a foreign affiliate. Once the agreement is in place, the American employer pays amounts equivalent to both the employer and employee shares of FICA on the affiliate’s behalf.³

Totalization Agreements

Because U.S. citizens working abroad can end up owing Social Security taxes in two countries on the same earnings, the United States has entered into “totalization agreements” with dozens of countries. These agreements assign coverage to one country’s system, using factors like the expected length of the foreign assignment, and they let workers combine credits earned under both systems to qualify for benefits neither would have paid alone.⁴

Who Counts as an Employee

IRC 3121(d) identifies several categories of workers who qualify as employees for FICA. The line matters because independent contractors pay their own Social Security and Medicare through self-employment tax, while employees split the tab with an employer.

Common Law Employees

The primary test is the common law standard. If the employer has the right to control what the worker does and how it gets done, the worker is an employee. The IRS looks at behavioral control (direction over when, where, and how the work is performed), financial control (control over the business aspects of the job), and the overall relationship between the parties.⁵

Corporate Officers

A corporate officer who performs services for the corporation is generally treated as an employee, even if the duties are minimal. The only exception is an officer who performs no services at all or receives no compensation.⁶

Statutory Employees

IRC 3121 also creates a special class of “statutory employees” who are treated as employees for FICA even if they might not pass the common law test. Four categories qualify:

Agent-drivers who distribute food, beverages, laundry, or similar products as agents or on commission.
Full-time life insurance salespersons whose principal business activity is selling life insurance or annuity contracts for one company.
Homeworkers who work on materials supplied by the employer according to the employer’s specifications.
Full-time traveling salespersons who solicit orders from businesses for merchandise intended for resale or for supplies used in the buyer’s business.

Statutory employee status applies only when three conditions are all met: the contract requires the worker to perform substantially all services personally, the worker has no substantial investment in the equipment or facilities used (other than transportation), and the services are part of a continuing relationship rather than a single transaction.¹

What Counts as Wages

Under IRC 3121(a), “wages” includes all compensation paid for employment, regardless of form. Salaries, bonuses, commissions, fees, and the cash value of non-cash compensation like lodging and meals are all wages.¹

The 2026 FICA rates and caps:

Social Security: 6.2% from the employee and 6.2% from the employer, applied only to the first $184,500 in wages.⁷
Medicare: 1.45% from each side, with no wage cap.²

Once an employee’s wages hit $184,500 for the year, the employer stops withholding the Social Security portion. Medicare withholding keeps going. The $184,500 cap, known officially as the contribution and benefit base, adjusts annually based on changes in the national average wage index.⁷

Common Exclusions from Wages

Not every payment an employer makes to or for an employee is taxable wages. IRC 3121(a) excludes employer contributions to qualified retirement plans, payments for group-term life insurance, employer-paid health insurance premiums, dependent care assistance up to statutory limits, and educational assistance. Reimbursements under an accountable plan, where the employee substantiates business expenses and returns any excess, are also excluded.

Tips

Cash tips of $20 or more in a calendar month are treated as wages under IRC 3121(a)(12)(B). The employee owes their FICA share on those tips, and under IRC 3121(q) the tips are deemed paid by the employer for purposes of the employer’s FICA obligation, even though the money came from customers.⁸

Mandatory service charges added to a customer’s bill are not tips. A payment qualifies as a tip only when the customer gives it voluntarily, decides the amount without employer interference, and chooses who receives it. Mandatory charges are ordinary wages, subject to regular withholding from the moment they are paid.⁸

Additional Medicare Tax

Since 2013, an extra 0.9% Medicare tax has applied to wages above $200,000 for single filers, $250,000 for married couples filing jointly, and $125,000 for married filing separately. The employee pays it all; there is no employer match. Employers must begin withholding the extra 0.9% once an individual employee’s wages pass $200,000 in a calendar year, regardless of filing status, because the employer has no way of knowing the employee’s household income.

The filing status thresholds come into play on the employee’s personal return, reported on Form 8959. An employee earning $190,000 whose spouse earns $80,000 owes the Additional Medicare Tax on $20,000 of combined wages (the amount over $250,000) even though neither employer withheld it. The couple covers the difference through estimated payments or by requesting extra withholding.

Work That’s Excluded from Employment

IRC 3121(b) lists categories of work that fall outside the definition of “employment” entirely, meaning no FICA tax is owed on the compensation. Several of these will not be obvious.

Family Employment

Services performed by a child under age 21 working for a parent are excluded from employment. So are services performed by one spouse for the other. A parent working for a son or daughter is also excluded, but only for domestic services or work outside the child’s trade or business, and even that exclusion has exceptions when the employer-child is a single parent or widowed person caring for a young child.⁹

The family exclusions apply only to sole proprietorships and partnerships where every partner is a family member. They do not apply if the employer is a corporation or an estate, even if the corporation is wholly owned by a family member. A parent who incorporates and then puts a teenage child on the corporate payroll owes FICA on those wages.

Student Workers

Services performed by a student enrolled and regularly attending classes at a school, college, or university, where the student works for that same institution, are excluded from employment under IRC 3121(b)(10). The IRS evaluates whether the employment is “incident to and for the purpose of pursuing a course of study” rather than career employment that happens to be at a school.¹⁰

Ministers and Members of Religious Orders

Service performed by a minister or member of a religious order in the exercise of their duties is excluded from the definition of employment. Ministers do not avoid Social Security entirely; they are treated as self-employed and pay the combined 15.3% self-employment tax, unless they file for an exemption based on religious conscience.¹

Farm and Household Workers

Farm workers and household employees are not exempt from FICA outright, but their wages are excluded until they cross specific dollar thresholds. For agricultural labor, an employer owes FICA if any single farm worker is paid $150 or more in cash wages during the year, or if total farm payroll (cash and noncash) reaches $2,500 for the year.² For domestic service — nannies, housekeepers, private cooks, and similar household workers — the 2026 threshold is $3,000 in cash wages paid to a single employee during the calendar year.¹¹ Below those amounts, the worker earns no Social Security credits for the job and neither side owes FICA.

Foreign Government and International Organizations

Services performed for a foreign government or a public international organization such as the United Nations or the World Bank are excluded from employment. The exclusion also covers services performed for an instrumentality of a foreign government, provided the worker is not a U.S. citizen or the services are of a type similar to those performed by foreign government employees in other countries.¹

Election Workers

Pay received by election workers — poll workers, ballot counters, and similar temporary election staff — is excluded from employment if it falls below a statutory threshold. That threshold has been $2,000 since 2021 and is subject to inflation adjustments.¹²

What Happens if an Employer Gets It Wrong

Misclassifying an employee as an independent contractor, or failing to withhold and deposit FICA, carries real financial consequences. The IRS can hold the employer liable for both the employer and employee shares of unpaid FICA taxes, plus penalties and interest.⁵

Trust Fund Recovery Penalty

The most severe consequence is the Trust Fund Recovery Penalty under IRC 6672. The employee’s share of withheld income tax and FICA tax is considered held “in trust” for the government. Any person responsible for collecting and paying over those taxes, which can include corporate officers, directors, controlling shareholders, and bookkeepers with check-signing authority, faces personal liability equal to 100% of the unpaid trust fund taxes if they willfully fail to pay them over. “Willfully” here does not require intent to defraud. Knowingly using the money to pay other creditors instead of the IRS is enough.¹³

Reduced Rates Under Section 3509

When an employer misclassifies a worker but had a reasonable basis for doing so and filed the required 1099 forms, IRC 3509 offers partial relief. Instead of the full employee share of FICA taxes, the employer pays a reduced rate, roughly 20% of the employee’s FICA obligation. That rate doubles to about 40% if the employer filed no information returns for the worker. Section 3509 relief disappears entirely for employers who intentionally disregard their withholding obligations.

Voluntary Classification Settlement Program

Employers who realize they have been misclassifying workers can apply for the IRS Voluntary Classification Settlement Program by filing Form 8952. The program lets them reclassify workers as employees going forward while paying only a fraction of the back taxes that would otherwise be owed. Eligibility requires consistent past treatment and no current IRS examination of the issue.⁵

Penalties for unpaid employment taxes follow the standard IRS structure: 0.5% of the unpaid amount for each month the balance is outstanding, capped at 25%, plus interest that accrues from the original due date.¹⁴

1
Office of the Law Revision Counsel. 26 US Code 3121 – Definitions
2
Internal Revenue Service. Publication 15 (2026), (Circular E), Employer’s Tax Guide
3
Social Security Administration. Internal Revenue Code Section 3121(l)
4
Social Security Administration. U.S. International Social Security Agreements
5
Internal Revenue Service. Worker Classification 101: Employee or Independent Contractor
6
eCFR. 26 CFR 31.3121(d)-1 – Who Are Employees
7
Social Security Administration. Contribution and Benefit Base
8
Internal Revenue Service. Revenue Ruling 2012-18: Tips Included for Both Employee and Employer Taxes
9
eCFR. 26 CFR 31.3121(b)(3)-1 – Family Employment
10
Internal Revenue Service. Student FICA Exception
11
Social Security Administration. Employment Coverage Thresholds
12
Internal Revenue Service. Election Workers: Reporting and Withholding
13
Internal Revenue Service. Trust Fund Recovery Penalty (TFRP) Overview and Authority
14
Internal Revenue Service. Failure to Pay Penalty