FROMONT BRIENS

[ARTICLE] Multi-country work and social security scheme, 2026/05/05

The internationalisation of career paths has never been so pronounced. Between secondments, expatriation, cross?border remote working, nomadic work and new forms of mobility, both companies and employees are operating in a legal environment that is constantly evolving.

To support companies through these changes, the International Mobility team at Fromont Briens, led by lawyers Sophie Pélicier?Loevenbruck, Pierre Sandres, Thomas Baudoin, Charles Dumel and Pierre Pomerantz, has launched the first edition of its newsletter dedicated to international mobility.

Below, you can find one of the articles from this inaugural issue (available here): To determine which social security scheme applies to a European Union national, it is necessary to identify the country in which their main activity is carried out. This assessment must consider not only activities performed within the European Union, but also those carried out in non?EU countries.

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Determining the applicable social security scheme for work carried out in several countries: activity outside the European Union must also be taken into account

CJEU, 11 December 2025, Case C-743/23

The Court of Justice of the European Union (CJEU) was asked to rule on a preliminary question concerning the interpretation of Article 13(1) of Regulation (EC) No. 883/2004, which governs the coordination of social security systems within the EU and with certain non?EU countries that have opted into the system, such as Switzerland.

This coordination requires the application of the legislation of a single Member State, even where a person carries out activities in several countries.

In such cases, the applicable legislation is that of the State of residence, provided that the individual performs a “substantial part” of their activity there. If no substantial part of the activity is carried out in the State of residence, other rules apply. For an employee working for a single employer (as was the case in this instance), the applicable legislation is that of the Member State in which the employer’s registered office or place of business is located.

The key issue concerned the definition of a “substantial part” of the employee’s activity. This concept is clarified by the implementing Regulation of 16 September 2009, which identifies working time and/or remuneration as indicative criteria. An activity is deemed substantial when it accounts for at least 25% of the overall activity.

In this case, the insured person, who resided mainly in Germany and was employed by a company headquartered in Switzerland, carried out work partly in Switzerland, partly via remote working from Germany, and partly in third countries not covered by the Regulation.

The individual initially applied for affiliation with the German social security scheme, and subsequently applied for mandatory health insurance in Switzerland. The German social security authority nevertheless took the view that German legislation applied, basing its decision solely on the time worked in Germany and Switzerland, and concluding that 50% of the activity was carried out in Germany.

The insured person challenged this decision, arguing that all activity, including that performed in third countries, had to be taken into account and that, in any event, they were already covered by the Swiss social security scheme during the period in question.

The referring court asked the CJEU whether activity in third countries had to be factored into the assessment. If only EU and covered countries were considered, 50% of the activity was indeed performed in Germany; if third?country activity was included, the share carried out in Germany dropped to 16%, excluding the application of German legislation.

The CJEU held that the insured person’s real situation must be assessed, taking into account all activities, including those performed in third countries. Focusing solely on activity within Member States would amount to a legal fiction disconnected from the reality of the work performed in the State of residence.

The Court therefore concluded that the individual did not carry out a substantial part of their activity in Germany and was consequently subject to Swiss legislation, as the country where the employer was established, even if the individual also carried out a substantial activity in a third country.

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