In February 2005, Illinois became the first U.S. state to grant home-based childcare providers (HBCPs) the right to form a labor union in order to bargain collectively with the state government. This policy inspired similar efforts across the country and represents a potentially important direction for childcare policy. To date, the implications of labor unions for the cost, type and availability of subsidized childcare has not been evaluated empirically. In this study, I examine the impact of granting Illinois home-based childcare providers the right to form a labor union on: (a) the type of childcare (licensed vs. license-exempt /home-based vs. center-based) used by subsidy-receiving Illinois infants and toddlers; (b) the per-child cost of subsidized childcare for infants and toddlers; and (c) the percentage of Illinois infants and toddlers who use childcare subsidies. To conduct these analyses, I combine data from the Current Population Survey with Childcare and Development Fund administrative records on U.S. infants and toddlers whose families received childcare subsidies during the period from 2002-2008. I employ a comparative case study by comparing the treated group to a "synthetic" control group generated using data on states that have not implemented childcare unionization. The synthetic-control group approach improves on traditional comparative case studies by providing a transparent, empirical approach for constructing the counterfactual, documenting comparison unit's contribution to the synthetically created control group and detailing the degree to which the synthetic control-group is, or is not, similar to the treated unit on pre-intervention measures of the outcome as well as on other selected characteristics. I find that, relative to the synthetic-control group, subsidy-receiving Illinois infants and toddlers spent an average of between 6.4 and 7-percentage points more care hours in licensed settings, as compared to license-exempt settings, in the three years following childcare unionization. I also find that relative to the synthetic-control group, between 0.7 and 1.1-percentage points fewer Illinois infants and toddlers used childcare subsidies after unionization. I find some indication that unionization led to a substantively important though not statistically significant $26 increase in the monthly-per child payments provided to care for subsidized infants and toddlers. (author abstract)