中文摘要
本文将Diamond（1980）模型扩展至包含工会的情形，以研究最优所得税，并分析在所得税得到优化时，工会是否有利于收入再分配。工会在各部门与企业就工资进行谈判，而企业单方面决定就业水平。在工会化劳动力市场中，最优失业救济金和最优所得税均较低。工会提高了收入再分配的效率成本，因为失业救济金和所得税会推高工资要求，进而造成非自愿失业。我们表明，只有当工会所代表的是其劳动参与在净额意义上受到补贴的（低收入）工人时，工会才具有社会合意性。工会通过形成对劳动的隐性税收，缓解所得税所造成的劳动力市场扭曲。我们自行编制了一个涵盖23个发达经济体18个行业的工会密度和参与税率数据集，并据此实证检验：（i）工会力量越强，参与税率是否越低；（ii）工会是否具有合意性。与理论预测一致，我们发现，工会力量越强，参与税率越低。此外，工会具有合意性的条件在实证中从未得到满足。针对荷兰的数值模拟证实，在所得税得到优化时，工会并不具有合意性；同时，工会力量越强，最优参与税率越低。
Abstract
This paper extends the Diamond (1980) model with labor unions to study optimal income taxation and to analyze whether unions can be desirable for income redistribution if income taxes are optimized. Unions bargain with firms over wages in each sector and firms unilaterally determine employment. Optimal unemployment benefits and optimal income taxes are lower in unionized labor markets. Unions raise the efficiency costs of income redistribution, because unemployment benefits and income taxes raise wage demands, and thereby generate involuntary unemployment. We show that unions are socially desirable only if they represent (low-income) workers whose participation is subsidized on a net basis. By creating implicit taxes on work, unions alleviate the labor-market distortions caused by income taxation. We empirically verify whether (i) participation tax rates are lower if unions are more powerful, and (ii) unions are desirable by compiling our own data set with union densities and participation tax rates for 18 sectors in 23 advanced countries. In line with our theoretical predictions, we find that participation tax rates are lower if unions are stronger. Moreover, the desirability condition for unions is never met empirically. Numerical simulations for the Netherlands confirm that unions are not desirable if income taxes are optimized and optimal participation taxes are lower if unions are stronger.