I study an effort by the Ecuadorian government to mitigate offshore tax avoidance through the imposition of an outflows tax. First, I find that the outflows tax led to a sharp decrease in dividend payments to tax havens. I document a decrease by 66% in dividend payments sent to tax havens relative to non-havens following an increase in the relative cost of transacting with tax havens by 5%. This drop is consistent with a net-of-tax elasticity of dividend payments abroad of 15. I find that exposed firms decreased overall dividend payments to all shareholders by 50% and increased retained earnings in the short run by 600%. This response was largely unaccompanied by any change in post-tax reinvestment behavior. Using administrative data on shareholder-company linkages to identify individuals highly connected to tax havens, I find that these individuals increased their domestic income reporting by 40% and paid 55% more in personal income taxes per year. This response was mainly driven by domestic capital income flows and independent labor income and not through repatriation behavior or wage labor income. These results suggest the substantial scope for countries to act unilaterally in mitigating tax haven use and increasing tax collections.