Citizenship can accelerate immigrant integration and result in benefits for both local communities and the foreign-born themselves. Yet the majority of naturalization eligible immigrants in the United States do not apply for citizenship and we lack systematic evidence on specific policies to encourage uptake. In this study we analyze the impact of a policy change by the United States Citizenship and Immigration Service (USCIS), the standardization of the fee waiver process in 2010. This reform allowed low-income immigrants eligible for citizenship to use a standardized form to have their application fee waived. We employ a difference-in-differences methodology, comparing naturalization behavior among eligible and ineligible foreign-born before and after the policy change. We find that the fee waiver reform increased the citizenship rate by 1.5 percentage points. This amounts to about 73,000 immigrants per year gaining citizenship who would not have applied otherwise. In contrast to previous research on the take-up of federal benefits programs, we find that the positive effect of the fee waiver reform was concentrated among the subgroups of immigrants with lower incomes, language skills, and education levels, who typically face the steepest barriers to naturalization. Further evidence suggests that this pattern is driven by immigration service providers, who help mostly poorer immigrants file the fee waiver request.