How do I know if my employer is considered a foreign affiliate for U.S. tax purposes?
Your employer is a foreign affiliate when it is a foreign entity in which a U.S. person (usually a parent corporation) owns more than 50% of the voting stock or value, directly or indirectly. The IRS definition sits in IRC Section 3121(l), and it matters for Social Security coverage, Form 5471 reporting, and W-2 eligibility.
Three practical tests signal foreign-affiliate status:
- A U.S. parent company owns more than 50% of the foreign entity
- The U.S. parent has entered a Section 3121(l) agreement, so U.S. Social Security and Medicare apply to American employees abroad
- You are paid through a foreign subsidiary but receive a U.S. W-2 covering FICA
Why it matters for your expat return:
| Scenario | FICA withheld? | SE tax risk | Form 5471? |
| Foreign affiliate with 3121(l) | Yes | None | Filed by U.S. parent |
| Foreign subsidiary, no 3121(l) | No | None (W-2 employee) | Filed by U.S. parent |
| Truly foreign employer (no U.S. ownership) | No | None (employee) | Not required |
| Self-employment contract | No | 15.3% unless totalization applies | Depends on structure |
If you are unsure, ask HR for a copy of your employment entity’s ownership chain and for confirmation of whether a Section 3121(l) agreement is in force.
Last updated on April 29, 2026
