Cross-Border Multiple Employment in Social Security Law

The Applicable Social Security Law Must Be Determined Based on Employment Exercised Worldwide

With its judgment dated 11 December 2025 (C-743/23), the European Court of Justice (ECJ) established a new standard in social security law:

Whether a person carries out a “substantial part” of their employment in their country of residence, thus making the social security law of that state applicable, is to be determined based on their worldwide employment activities.

Background

To determine the applicable social security law for cross-border employment within the EU, the EEA, and Switzerland (the "Member States"), Regulation (EC) 883/2004 and the Implementing Regulation (EC) 987/2009 apply. If a person ("employee") usually carries out employment in two or more Member States (so-called multiple employment), only one Member State’s social security law applies according to Art. 11(1) and (3)(a) in conjunction with Art. 13(1) of Regulation (EC) 883/2004.

• If a person carries out a "substantial part" of their employment in their state of residence, the social security law of the country of residence applies (Art. 13(1)(a) Regulation (EC) 883/2004).
• If this is not the case, depending on the circumstances (number of employment relationships – self-employed activities are excluded, registered office of the employer(s), see Art. 13(1)(b) Regulation (EC) 883/2004), a different social security law may apply.

“Substantial Part”

Whether a “substantial part” of the employment is carried out in the country of residence is generally determined by an overall assessment. Art. 14(8) of Regulation (EC) 987/2009 clarifies: An employee exercises a "substantial part" of their employment in their country of residence if at least 25% – measured by working time and remuneration – is performed there.

A point of contention was which working times should be considered for the 25% threshold:

• Only activities within the Member States, or
• also activities outside the Member States (so-called third countries)?

Previous Interpretation and Administrative Practice

Previously, only working times exercised by an employee within the territorial scope of Regulation (EC) 883/2004 were considered, while third-country activities were disregarded. If at least 25% of the employment performed within the Member States took place in the country of residence, the social security law of the country of residence applied (including both employment and self-employment), and, for example, the social security law of the employer’s location did not apply.

This interpretation was justified by the territorial limitation of the relevant regulations to the Member States; reference to third countries was considered system-foreign.

New Interpretation – ECJ Judgment

The ECJ has now decided that all working times exercised worldwide – including in third countries (outside the Member States) – must be taken into account when determining the 25% threshold.

The concept of "activity" pursuant to Art. 13(1) Regulation (EC) 883/2004 and Art. 14(8) Regulation (EC) 987/2009 is not territorially restricted.

Practical Consequences – Example

This new interpretation can have significant practical consequences.

Example: A sales employee residing in Germany works for a company based in Switzerland, focusing on international sales, mainly in Asia. According to Swiss social security law, this is an employment. The planned distribution of working hours is as follows:

• approximately 80% business trips to customers in various Asian countries,
• approximately 10% office work from the home office in Germany,
• approximately 10% presence at the employer’s location in Switzerland.

Previous Assessment

Previously, 80% of the working time (third-country activity) was not considered in the determination of the applicable social security law; only Germany and Switzerland were taken into account, resulting in 50% attributed to the country of residence (Germany). German social security law would therefore apply, and the Swiss employer would have to pay contributions into the German social security system.

New Assessment

As a result of the ECJ’s decision, working times in Asia must now be included. Taking this worldwide perspective, the employee works only 10% in their country of residence. Therefore, they do not perform a "substantial part" of their employment in Germany. Accordingly, German social security law no longer applies; instead, Swiss social security law as the law of the employer’s location applies (Art. 13(1)(b)(i) Regulation (EC) 883/2004). The employer must therefore pay social security contributions into the Swiss system.

Impact on Existing A1 Certificates

If the applicable social security law for multiple employment has already been determined and an A1 certificate has been issued, it continues to be binding within its period of validity, unless withdrawn or revoked by the issuing authority.

In cases of multiple employment, A1 certificates are normally limited to a maximum of 12 calendar months to ensure regular assessment (Art. 14(10) Regulation (EC) 987/2009). Before expiry, if multiple employment continues, a new application must be filed; the worldwide approach will now be applied during reassessment.

Final Evaluation

Formally, this is an accurate and welcome interpretation of existing law. In practice, however, the judgment marks a departure from previously widespread administrative practice, at least by the German social security authorities.

The judgment creates legal clarity: For the social security determination in cases of multiple employment, the worldwide employment exercised by a person is decisive. This global perspective cannot be applied to self-employment, as the ECJ explicitly points out.

Employers and employees should therefore review and, if necessary, restructure existing and future cross-border employment models, especially those with third-country components, if maintaining a specific social security law is desired.