The main purpose of this article is to present the concept of the cross-border conversion of a company and the possibilities for companies to carry it out under the freedom of establishment in the light of the recent judgment of the CJEU in case C-106/16 Polbud, and the provisions of Directive 2019/2121 EU of the European Parliament and of the Council of 27 November 2019 amending Directive (EU) 2017/1132 as regards crossborder conversions, mergers and divisions, which should be implemented by the Member States by 31 January 2023. The article discusses selected aspects of the procedure of cross-border conversion of a company, regulated in new Directive 2019/2121, and focuses on the scrutiny of legality of cross-border conversion of a company by competent national authorities. Particular attention is paid to the concept of abuse of law in the context of the possibility for national authorities to issue a pre-conversion certificate as the precondition for registration of the company undergoing conversion in the Member State of destination.