We analyze the impact of tax morale on optimal progressive labor income taxation. Only
universal basic income is financed from a linear tax and the financing of public goods is
neglected. Each individual supplies labor and (un)declares earning, depending on his labor
disutility and tax morale. Limiting the utilitarianism to the poorer parts of the population
(defined by the inclusion share), the optimal tax rate is an increasing function of the tax
morale and a decreasing function of the inclusion share, provided that the average wage
of those included is higher than 0.54 times the average wage