This article aims to delineate the content and limits of the duty to protect the European Union’s financial interests regarding tax-based own resources, namely customs duties and VAT, which are key for financing the EU budget. It specifically addresses the duties of the EU Member States to make these resources available to the Union and to combat fraud and other illegal activities impacting their effective collection. Yet, these duties must be exercised in compliance with the protection of fundamental rights. The conflicts arising from the limits imposed by national rights and those enshrined in the EU Charter are also critically addressed.