We investigate the causal impact of unfair chances and gender discrimination on labor supply decisions. We conduct a large-scale experiment in which workers individually engage in the same task for a fixed piece-rate wage. We employ two payment schemes with equal wages, and three payment schemes with unequal wages generated through different procedures: (1) fair chances, (2) unfair chances based on an unspecified source, and (3) unfair chances based on gender discrimination. We find that, at a given wage, negative gender discrimination reduces the labor supply of workers substantially compared to equal wages (-22%). This effect is twice as large as the decrease induced by unequal wages from non-discriminatory fair and unfair chances (-11%). Moreover, the unfairness of non-discriminatory chances does not influence labor supply. Advantaged workers do not react to the unequal wages generated by our different procedures. Overall, our results support a novel supply-side consequence of discrimination in labor markets.