Under the agreement, a detached worker remains subject only to the social security
taxation and coverage laws of the country from which the employer transfers him or
her from or the country the worker transfers their self-employment from provided that
the worker meet all the following conditions:
The employer or worker expects the period of work in the host country to last no more than five years. The five-year period begins with the date the work in the host country
begins or July 1, 1984 (the effective date of the agreement), whichever is later.
The employment relationship (in the case of employment) or the business activity (in
the case of self-employment) existed before the worker transfers from the home country; and
If an American employer sends an employee to become an employee of the company’s affiliate
in Belgium, the American employer must have entered into an agreement with the Internal
Revenue Service (IRS) under section 3121(l) of the IRS Code. The 3121(l) provides
social security [recommend using lower case] coverage for U.S. citizens and residents
employed by the affiliate. In such cases, the employer must still obtain a certificate
of coverage to establish the exemption from Belgian social security taxes.
NOTE: The detached worker rule may apply even if the worker does not go directly from one
country to the other but first works in a third country.