More and more cross-border workers are combining several professional activities: salaried employment in one or more countries, and self-employed work in another. In such situations, the question of social security affiliation is crucial, as European law imposes a strict rule: only one system of social security legislation can apply at any given time.
It is in this context that the concept of marginal activity comes into play. Often poorly understood, it can nevertheless have a real impact on determining the competent state for social security purposes.
Principle: social security contributions in a single country
In all situations involving the combination of professional activities in several countries, European law establishes a fundamental principle: a person may be affiliated with only one social security system at a time and must therefore contribute in only one country, but on all of their income. It is therefore never possible to pay contributions simultaneously in two countries for the same period. Priority rules have been put in place to determine the competent State.
Marginal activity
European law has introduced the concept of marginal activity. An activity is considered marginal when it is purely ancillary, both in terms of time and income. As an indication, an activity representing less than 5% of total working time or overall remuneration may be regarded as marginal. This assessment is carried out on a case-by-case basis, taking into account the actual circumstances of the situation.
Once an activity is considered marginal, it is disregarded when determining social security affiliation.
Impact in cases of holding two employed positions
Dual salaried employment
When a cross-border worker carries out two salaried activities in two different States, the main criterion is the place of residence. If a substantial part of the activity is performed in the State of residence — in practice at least 25% of working time or remuneration — affiliation is established in that country. Based on these criteria, there can be no marginal activity.
Employee and civil servant
When a person works as a civil servant in one State and combines this activity with salaried employment in another State, European law generally provides for affiliation to the social security system of the State to which the employing administration belongs. Civil servant status constitutes the primary connecting factor. However, this rule applies only if the activity performed as a civil servant is genuine and not marginal. If the civil servant activity is purely ancillary, both in terms of working time and remuneration, it may be classified as marginal and disregarded in the analysis. In such a case, affiliation is no longer determined by civil servant status, but by the salaried activity carried out in the other State, in accordance with the general rules applicable to employees engaged in cross-border work.
Impact in cases of holding both a salaried and a self-employed activity
The logic is different when a worker is both salaried in one country and self-employed in another. In this situation, the existence of a salaried activity generally leads to affiliation with the social security system of the State where that dependent employment is carried out.
However, if the salaried activity is marginal (very low in terms of time and income), it is not taken into account when determining the applicable system. In that case, affiliation is determined as if the person were primarily self-employed: the rules specific to self-employment are applied, based on the country in which the activity is actually carried out.
Practical information
The classification of an activity as marginal does not depend on the choice of the employee or the employer. It is assessed by the competent social security authorities, based on the information provided.
An incorrect assessment of the situation can have significant consequences, such as calls for back contributions, retroactive adjustments, or difficulties in accessing social benefits. In case of doubt, it is therefore recommended to contact the competent social security authorities, in particular the CLEISS (French Centre for European and International Social Security Liaison).
To safeguard their situation, cross-border workers should precisely document the reality of their activities including working hours, level of remuneration, geographic distribution, and legal nature and, in the case of complex multiple activities, anticipate the question of affiliation by requesting, if necessary, a formal determination of the applicable legislation under the European mechanisms.
