The paper addresses the introduction of a unique persistent identifier in the context of the proposed reform of the eIDAS Regulation, exploring its implications in light of the fundamental right to personal data protection recognized by EU primary law. The new identifier aims to enhance identification accuracy and trust in the European Digital Identity Wallet envisaged by the eIDAS Proposal. However, it raises concerns vis-à-vis the principles of data protection by design, purpose limitation, and data minimization. It is suggested that these three principles, read together, set clear boundaries for the EU legislator when deciding the techniques used for the functioning of the European Digital Identity Wallet. The paper argues that the new identifier is not in line with the right to personal data protection, is at risk to be at odds with some Member States Constitutions, and concludes by proposing some possible ways forward.