Free movement, equal treatment and citizenship of the Union

The prohibition of discrimination, at least on grounds of nationality, has always been a constitutional principle of Community law. Such discrimination can take many forms, since Community law prohibits not only direct discrimination but various forms of indirect discrimination. Furthermore, the Court of Justice has indicated that where discrimination on grounds of nationality is in issue, the requirement of proof is not a heavy one on the complainant. All that is needed to place the burden on the respondent to justify the potentially differential treatment is that complainants show that the requirement applied to them is intrinsically likely, or susceptible by its very nature, to affect them adversely in comparison with the State's own nationals. The modern formulation of the prohibition of discrimination recognizes that protection from discrimination on grounds of nationality is central to the concept of citizenship of the Union. [Taken from Introduction]