Purpose - To explore state employee union density, this paper discusses determinants of state sector union density and then empirically examines the linkages of the determinants and state union membership in the USA. Design/methodology/approach - After operationalizing and measuring the indicators of the crucial determinants of state employee union density, this study conducts a cross-sectional analysis on state sector union density. The dependent variable used in this study is state employee union density in the USA. The independent variables used in this study are the presence of a liberal state government, the presence of collective bargaining laws, the size of a budget deficit, and an unemployment rate which could determine state sector union density. Findings - This study finds that state union density is not determined by the size of budget deficits and the presence of liberal governors but by the presence of collective bargaining laws and liberal state legislatures and unemployment rates. Additionally, this study reveals that unified governments can make a difference in state employee union density. For instance, liberal states controlling both the state executive and legislative branches have a positive impact on state employee union density, while conservative states ruling both branches have a negative impact on state union density. Originality/value - This paper analyzed pooled cross-sectional data on state employee union density in the US with regards to crucial legal, political, financial, and economic variables.