As regards social insurance, there is applicable the basic principle according to which, at any given time, it is possible to be liable to social insurance only in one country. Therefore, even if an activity is carried out simultaneously in several Member States, the insurance is kept only by one country, and it is necessary to pay all contributions to social insurance in this country.
In respect of territorial competence, it should be:
- the country where your place of residence is - if you perform a substantial part of your work in this country;
- the country where the centre of interests of your business is located - if you do not reside in the country where you perform a substantial amount of work.
In order to determining whether a substantial part of activity is performed in a particular country, it should be considered the generated turnover or income, working time, and a number of provided services. A document stating where the contributions should be paid is the A1 form. The model A1 form is identical throughout the European Union; on its basis contributions are paid in a given EU country, and there is also obtained an exemption from the obligation to pay those contributions in another country.
As a result, within the framework of rendering cross-border services in Poland, service providers are not required to register their business in the social insurance system. A service provider is only required to apply to the insurance institution in his country, competent for his place of residence, for a social security certificate (A1 form). The obtained certificate should be presented, if necessary, to an employee of the Social Insurance Institution, e.g. in the course of an inspection.
More information is included in the ZUS guide (in particular, on pages 14-15 of the guide).