This study investigates the impact of competition from informal or unregistered firms on the likelihood of formal manufacturing small and medium-size enterprises obtaining internationally recognized quality certificates. The sample includes 16 countries in Latin America and the Caribbean, one of the regions with the highest levels of informality in the world. The study uncovers a positive impact, with a one standard deviation increase in informal competition leading to an increase in the probability of having a quality certificate by 2.9 to 3.6 percentage points across the different specifications. This effect is large, given that only 10.4 percent of small and medium-size enterprises have a quality certificate. These findings are consistent with the "legalist" model of informality, whereby the positive impact of informal competition on the likelihood of having a quality certificate is significantly larger in countries where the business environment is less favorable to operating in the formal versus informal sector due to factors such as the weaker rule of law and greater regulatory burden on formal firms. The paper provides several layers of checks against omitted variable bias, reverse causality, and measurement errors. The findings also show that, as expected, there is no statistically significant impact of informal competition on the likelihood of having a quality certificate among large manufacturing firms.