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(Tele-)work performed simultaneously within the EEA: what changes with the Moguntia ruling?

24/03/2026

International News

by Mehdi Warnier Julie Rousseau

Introduction

European rules governing the determination of the applicable social security legislation for employees performing activities in several Member States can be complex. The Court of Justice of the European Union (CJEU) is regularly called upon to clarify the practical application of these rules. With its ruling in Moguntia / GKV‑Spitzenverband (C‑743/23), the Court confirms that all professional activities must be taken into account – including those carried out outside the European Union.


This decision is not limited to traditional cross-border situations: it also affects the application of the European Framework Agreement on Telework (2023), particularly the interpretation given by the NSSO. This article first recalls the general principles before examining the scope of the ruling and its practical consequences.

1. General principles

The determination of the applicable legislation is based on Regulations (EC) No. 883/2004 and 987/2009. The fundamental rule remains lex loci laboris: every employee is subject to the legislation of the State in which the activity is performed. The Regulations nevertheless provide specific rules to avoid a person being subject to several social security systems for a single employment relationship.


In cases where activities are carried out in several Member States, this may involve either posting or simultaneous activity. This article focuses solely on simultaneous activity.

2. Simultaneous activity: definition and scope

An employee is engaged in simultaneous activity when they “normally” perform activities in at least two Member States. This covers:

  • the separate performance of activities in several States, even if occasional;
  • the permanent alternation of activities between several States.


Marginal activities (< 5% of working time or remuneration) are excluded from the analysis.

Example: An employee residing in Belgium works:

  • three days per week from home in Belgium (+/- 60%);
  • two days per week from the employer’s office in France (+/- 40%),
  • occasionally in Luxembourg (a few days per year, i.e. < 5%).


Although three countries are involved, the activities performed in Luxembourg are marginal and are therefore excluded from the analysis.

3. Applicable legislation and the notion of substantial activity (25%)

Regulation 883/2004 distinguishes two cases, depending on whether the employee is employed:

  • For a single employer:
    • if the employee performs substantial activity in their State of residence (≥ 25%), they are subject to that State’s legislation;
    • otherwise, the legislation of the employer’s registered office applies.
       
  • For several employers:
    • the distribution depends on whether substantial activity is performed in the State of residence and on the location of the employers.
    • an activity is substantial when it accounts for at least 25% of working time and/or remuneration.

Example: An employee residing in Belgium and employed by a French company performs 45% of their working time in Belgium, 5% in Luxembourg and 50% in France for the same employer. They will be subject to Belgian social security, since they reside and perform substantial activity there.


Example: Conversely, if that employee performed only 20% of their time in Belgium, they would no longer be performing substantial activity in the State of residence and would therefore fall under French legislation, as State in which the employer is situated.

4. The Moguntia ruling

Until now, several authorities — including the Belgian NSSO — neutralised activities performed in third countries (outside the EEA/Switzerland). Administrative practice consisted of ignoring work in third countries and recalculating percentages solely on the basis of “European activities”.


The Moguntia ruling brings a major shift: salaried activities performed in a third country must mandatorily be included in the overall assessment when they are intrinsically linked to activities within the EEA/Switzerland. Neutralization is no longer permitted.


The CJEU insists on a strict reading of Regulation 987/2009, which requires consideration of all professional activities in a “global assessment”.


The ruling aligns with established case law requiring full consideration of the employee’s real situation and all activities performed to determine applicable social security legislation. The Court also emphasises the wording of Article 14(8) of Regulation 987/2009, which refers to “all” of the employee’s activities as part of a “overall assessment” of their situation. According to the Court, failing to take the full situation into account would amount to creating a legal fiction detached from the practical reality.

Example: In a situation where an employee residing in Belgium and employed by a company established in France performed 20% of their working time in Belgium, 60% in France and 20% in the United States, the NSSO considered the employee to be employed according to a 25% / 75% distribution within the EEA/Switzerland — with the time worked in the United States being ignored. The employee was therefore subject to Belgian social security, since they reside there and perform a substantial part of their working time there (≥ 25%).


The ruling now requires that periods of work performed in third countries be included in the total calculation, meaning that no substantial activity remains in the State of residence (≤ 25%). This leads to the application of the legislation of the State where the employer is established, namely France.

5. Consequences for Belgian practice and the Telework Framework Agreement

Previously, the NSSO recalculated percentages based only on activities within the EEA/Switzerland. This is no longer permitted.


The impact is direct on the 2023 European Framework Agreement on Telework, which aims to stabilise structural cross-border telework situations for employees who:

  • work for an employer located in another State;
  • telework regularly from their State of residence.


The agreement allows the continued application of the employer’s State legislation even if telework exceeds 25%, provided that:

  • telework in the State of residence does not exceed 50%;
  • the situation remains strictly bilateral, meaning that work is performed in only two signatory States to the Framework Agreement: the employee’s State of residence and the employer’s State.


The Moguntia ruling now requires that any activity performed in a third country be taken into account. As a result, an employee who performs regular salaried work in a third country that is intrinsically linked to their simultaneous activity within the EEA/Switzerland can no longer fall under the Framework Agreement, since work would then be carried out in more than two countries. Only marginal activities in third countries could still allow the agreement to apply.

Example: An employee performed 40% of their working time in Belgium through telework, 50% in France where the employer is located, and 10% in the United States, all within the framework of the same employment relationship.

Before the Moguntia ruling, these activities outside the EEA/Switzerland were neutralised by the NSSO, and the situation was treated as strictly bilateral. The Framework Agreement could therefore apply, and the employee remained subject to French social security.

Following the Moguntia ruling, this situation no longer meets the “bilaterality” requirement. The NSSO will no longer accept the application of the Framework Agreement. In this case, the employee falls back on the “basic rules” and becomes subject to Belgian social security legislation (their State of residence), since they perform a substantial part of their work there (≥ 25%).

As of today, the other authorities of the signatory States have not yet communicated their position, but they can logically be expected to interpret the Framework Agreement in the same way.

Conclusion

The Moguntia ruling confirms a clear evolution in the case law of the CJEU: any social security assessment in situations of simultaneous employment must accurately reflect the employee’s full professional reality, without artificially excluding activities performed outside the EEA/Switzerland.


This decision results in a major adjustment of administrative practice:

  • the end of the neutralisation of activities in third countries;
  • the systematic inclusion of 100% of the employee’s actual activity;
  • a de facto restriction of the scope of the Telework Framework Agreement, which can no longer apply to employees who perform regular salaried activities in a third country.


These developments require employers to carefully reassess their organizational models and international working arrangements, as these rules may have significant consequences for the determination of the applicable social security legislation.


Regular missions in third countries, insofar as they constitute habitual and inherent activities within the employee’s overall employment, may in particular suffice to exclude the application of the Framework Agreement and have significant implications for the determination of the applicable social security legislation.