Under Regulation (EC) 883/04, if an employee works simultaneously in several EU member states, a substantial part of which is in his state of residence, in principle, the social security legislation of the state of residence applies.

Recently, the Dutch Central Appeals Tribunal ruled on the situation of an employee who worked a substantial part of his time from home in his state of residence, while the employer was established in another member state.  

According to the Central Appeals Tribunal, the legislation of the state of residence then only applies if the employer has expressly or tacitly agreed to work from home in the other member state. In other words, the work pattern as such, is not decisive.

As this ruling seems to go slightly further than previous European Court of Justice rulings, we cannot rule out that other EU member states may reach a different conclusion.