Labor market competition is considered a key factor in explaining attitudes toward immigrants. Nonetheless, scholarship in this area, especially in the context of south-south migration in Latin America, has yet to test this proposition directly. In general, scholars use education as a proxy for labor market skills, testing whether unqualified workers drive xenophobic attitudes. We claim this approach could be insufficient, as we do not know whether low-skilled workers are directly affected by immigrant workers. We argue that informal native workers in the Global South can feel more strongly the labor market competition from migrants because their jobs are less secure and they might not be eligible for any welfare program if they were to lose their source of income. In this article, instead of using education, we use primary data to measure informality in the labor market in Colombia, using a battery of indicators. Then, using a conjoint experiment, we test whether informal workers hold more adversarial attitudes toward immigrants compared to workers in the formal sector.