When redistribution leads to regressive taxation

We introduce labor contracts, in a framework of optimal redistribution: firms have some local market power and try to discriminate among heterogeneous workers. In this setting we show that if the firms have perfect information, i.e, they perfectly discriminate against workers and take all the surplus, the best tax function is flat. If the firms have imperfect information, i.e, if they offert incentive contracts, then (under some assumptions) the best redistributive taxation is regressive.