Prior to the reform, about 90 percent of the personal tax base consisted of labor income. Statutory marginal tax rates on labor income were very high, even at relatively low income levels, especially after the revolution. The large number of tax exemptions and fiscal benefits, together with high marginal tax rates, entailed the progressive erosion of the tax base through tax avoidance. Furthermore, Portuguese membership in the EC created the imperative for a number of changes in the tax system, especially the introduction of the value-added tax.