The citizenship of the Union, established by the Maastricht Treaty, became, by virtue of CJEU case law, a fundamental status of nationals of the Member States enabling those who find themselves in the same situation to enjoy the same treatment in law irrespective of their nationality. The paper aims to research how the CJEU expanded the EU law application by using the citizenship of the Union and where it set the limits to this expansion. To this end, following the introductory part of the paper, the issues of acquisition and loss of Union citizenship have been analysed. The third part of the paper researches into the CJEU case law regarding expansion of EU law application through the citizenship of the Union. This expansion was first conducted by eliminating both economic and cross-border links as conditio sine qua non of EU law application. The fourth part of the paper considers the possibility of emancipation of EU citizenship from the concept of Member State nationality regarding relevant TEU and TFEU provisions and CJEU case law. Finally, the paper concludes that CJEU has greatly encouraged the expansion of citizenship of the Union but has also limited this expansion by attaching it to national citizenship, which is in line with relevant TEU and TFEU provisions.