Where an employee works in more than one member state (meaning, in this context,  a country that is part of the European Economic Area plus Switzerland) on a regular basis, the basic rule is that they are covered by the social security system in their country of residence if they carry out a substantial part of their activities in that country. However, if this test is not met, the social security liability reverts to the state where the employer is based. For detailed guidance, see the European Union’s website.  

In this context, ‘substantial’ means at least 25% of either working time or remuneration. When determining whether the 25% test is met, it was previously  assumed that any working time and remuneration relating to employment in countries that are not member states – referred to as ‘third countries’ – could be ignored. However, this has been called into question by the Court of Justice of the European Union (CJEU) in a ruling released on 11 December 2025 (Case C‑743/23). 

CJEU ruling 

The CJEU was asked to give a preliminary ruling in proceedings between an individual and GKV-Spitzenverband (Germany’s Health Insurance Fund). The individual was employed by an employer established in Switzerland and carried out his employment duties in  Germany, where he lived, as well as in Switzerland and in third countries. Ignoring his employment in third countries, GKV-Spitzenverband treated the individual as subject to the German social security scheme as the 25% working time threshold was met.   

However, the CJEU found that this was incorrect: an employee’s activities in a third country should be taken into account in the same way as their activities in a member state. As a result, the proportion of working time spent in Germany did not meet the 25% threshold meaning the social security liability falls to where the employer is based, ie Switzerland. 

Possible implications 

Several EU member states have consistently assessed working time in such cases by excluding the time spent (or remuneration relating to) working in third countries, with the understanding being that the EU social security legislation cannot apply to third countries. The same interpretation has also been applied to the Framework Agreement for cross-border teleworking, which was introduced to simplify the social security position for remote workers post pandemic. The ruling suggests that several scenarios involving multi-state workers may have been incorrectly assessed for social security purposes.  

This change may have an impact on the current application forms for A1 certificates, which do not currently collect information on third country working time. Any modifications would be implemented separately by each member state as there is currently no uniform process.  

It is unclear as to what the implications may be for the UK under the EU-UK protocol. However, as the rules generally mirror the EU coordination rules, it may be that the same approach is adopted especially where an individual is working in more than one member state and the UK. Employers and their advisers may wish to consider if any employees could be affected and assess whether any changes may be required to processes going forward.