This article examines the legality of unilateral secondary sanctions under international law, focusing on their potential characterization as breaches of peremptory norms (jus cogens) and the resulting duty of non-recognition. Unlike primary sanctions, which are typically grounded in territorial or nationality-based jurisdiction, secondary sanctions operate extraterritorially by targeting third-state actors that maintain lawful relations with a sanctioned state. Their expanding use raises serious concerns regarding state sovereignty, non-intervention, and the limits of jurisdiction. Drawing on the jurisprudence of the ICJ and the ILC’s Draft Articles on State Responsibility, the article argues that secondary sanctions are structurally prone to conflicting with fundamental principles of international law. In certain circumstances, particularly where they produce grave and systematic humanitarian consequences, such measures may implicate obligations erga omnes and even amount to serious breaches of peremptory norms, including the prohibition of unlawful intervention or crimes against humanity. In such cases, Article 41 of the ILC Articles gives rise to an obligation of non-recognition by third states. The article distinguishes between domestic blocking statutes and the international legal duty of non-recognition, contending that the latter derives from the hierarchical structure of the international legal order. It concludes that clearer normative frameworks are required to reconcile foreign policy objectives with jus cogens and the protection of fundamental rights.