As noted earlier, certain types of income such interest on state and local bonds are treated preferentially by the tax system. This makes it possible for some high income households to have little or no tax liability. In 1969 the Secretary of the Treasury set off a political firestorm when he announced that 155 individuals with income above $200000 had paid on federal income tax several years earlier. The alternative minimum tax, enacted in 1969 and modified several times since than, was an attempt to ensure that rich people who benefited from various tax shelters paid at least some tax.