A simulation model of an open economy with a unionized labour market i
s set up to analyze the effects of a labour tax reform which combines
cuts in marginal tax rates with measures to broaden the tax base. We f
ind that such a reform will be contractionary and welfare reducing if
unions set wage rates with the purpose of maximizing the after-tax inc
ome of their members. By contrast, if unions also allow for the disuti
lity of work of their members, the reform will stimulate employment, i
ncrease the welfare of all generations, and redistribute welfare in fa
vour of future generations.