We investigate how the composition of expenditure shapes the transmission of monetary policy in a currency union. European Monetary Union data reveal three facts: (1) higher inequality countries have larger service expenditure shares; (2) monetary policy has a weaker output impact in these high-service-share, high-inequality countries; and (3) monetary policy induces systematic trade flows between high- and low-service-share countries. We develop a New Keynesian model with non-homothetic preferences and heterogeneous sectoral income that rationalizes these facts. Pro-cyclical inequality, driven by wealthier households' greater income exposure to services, buffers poorer households' consumption to contractionary shocks, dampening overall policy transmission. Our findings suggest that accounting for cross-country differences in consumption and income distributions is essential for understanding common monetary policy.