Is the optimal labor income tax progressive in a unionized economy?

This paper concerns optimal nonlinear labor income taxation in an economy with union wage setting and endogenous hours of work. The purpose is to study the determinants of tax progression. We show that the optimal degree of progression of the labor income tax depends on the extent to which the government can influence the wage rate via tax policy as well as on its ability to redistribute income across individuals. In addition, the argument for progressive labor income taxation depends on whether hours of work are chosen by the employed themselves or the union.