The article focuses on the impact the case law of the Court of Justice of the European Union on frontier workers regime. Cross-border commuters embody a specific category of migrant workers, characterized by a double link with the State of employment and with the State of origin. The key question is whether the Member States of employment are entitled to impose integration requirements as a condition to grant social advantages to workers who reside elsewhere, in order to avoid excessive financial burdens. The analysis examines the genuine link and the right-to-reside tests developed by the Court of Justice in relation to economically inactive EU citizens and highlights a trend towards their "de facto" extension to frontier workers. The article contends that such an approach reflects a gap between the formal definition of workers under EU law and the actual protection granted to weaker categories of migrant workers, to the detriment of the principle of non-discrimination.