Marginal tax rates
"Because marginal tax rates affect real output, they also affect government revenue. An increase in marginal tax rates shrinks the tax base, both by discouraging work effort and by encouraging tax avoidance and even tax evasion. This shrinkage necessarily means that an increase in tax rates leads to a less than proportional increase in tax revenues. Indeed, economist Arthur Laffer (of “Laffer curve” fame) popularized the notion that higher tax rates may actually cause the tax base to shrink so much that tax revenues will decline, and that a cut in tax rates may increase the tax base so much that tax revenues increase."