The present paper examines the effect of unions and other civil society groups on social policy in South American democracies. Long-term effect of such organized groups will be measured through levels of social expenditure; and contextualized influence will be measured observing the process of structural reforms (or lack thereof) in Argentina and Brazil in the health and pension sectors. This analysis shows that both partisanship and union strength matter in the expansion period for social security spending and pension reform processes. Alternatively, in determining spending on human capital and health reforms, the role of organized labor and other social groups is the key variable to understand social policy change. This study seeks to improve upon previous work by testing whether welfare state theories travel to South America to explain differences in the depth of social policy changes. Additionally, it innovates by assessing the independent effect of unions on social policy since the return of democracy to the present and by combining quantitative and qualitative research strategies, namely a modified random effects pooled time series and a case study comparison.