A little history lesson on the Federal Income Tax. There are some good web-sites on the topic, including http://taxhistory.tax.org and http://www.taxworld.org/History/TaxHistory.htm that contains:
The Tax Act of 1861 proposed that "there shall be levied, collected, and paid, upon annual income of every person residing in the U.S. whether derived from any kind of property, or from any professional trade, employment, or vocation carried on in the United States or elsewhere, or from any source whatever."
The 1861 Tax Act was passed but never put in force. Rates under the Act were 3% on income above $800 and 5% on income of individuals living outside the U.S.
The Tax Act of 1862 was passed and signed by President Lincoln July 1 1862. The rates were 3% on income above $600 and 5% on income above $10,000. The rent or rental value of your home could be deducted from income in determining the tax liability. The Commissioner of Revenue stated "The people of this country have accepted it with cheerfulness, to meet a temporary exigency, and it has excited no serious complaint in its administration." This acceptance was primarily due to the need for revenue to finance the Civil War.
Although the people cheerfully accepted the tax, compliance was not high. Figures released after the Civil War indicated that 276,661 people actually filed tax returns in 1870 (the year of the highest returns filed) when the country's population was approximately 38 million.
The Tax Act of 1864 was passed to raise additional revenue to support the Civil War.
Senator Garret Davis, in discussing the guiding principle of taxation, stated "a recognition of the idea that taxes shall be paid according to the abilities of a person to pay."
Taxes rates for the Tax Act of 1864 were 5% for income between $600 and $5000; 7.5% for income between $5001 and $10,000; 10% on income above $10,000. The deduction for rent or rental value was limited to $200. A deduction for repairs was allowed.
With the end of the Civil War the public's accepted cheerfulness with regard to taxation waned. The Tax Act of 1864 was modified after the war. The rates were changed to a flat 5 percent with the exemption amount raised to $1,000. Several attempts to make the tax permanent were tried but by 1869 "no businessman could pass the day without suffering from those burdens" The Times. From 1870 to 1872 the rate was a flat 2.5 percent and the exemption amount was raised to $2,000.
The tax was repealed in 1872 and in its place was installed significant tariff restrictions that served as the major revenue source for the United States until 1913. In 1913 the 16th Amendment was passed, which allowed Congress authority to tax the citizenry on income from whatever source derived.
It should be noted that the Tax Act of 1864 was challenged several times. The Supreme Court unanimously supported the tax. After the war the tax was declared unconstitutional by the same court because it represented direct taxation on the citizenry which was not allowed under the constitution.
and http://encarta.msn.com/find/concise.asp?mod=1&ti=0332F000&page=4#s45 that contains:
"In 1913 the states ratified the 16th Amendment to the Constitution, which authorized Congress to tax the incomes of citizens. In late 1913 Congress instituted a restricted tax on personal income, with a maximum rate of 7 percent."
That 7 percent maximum rate seems to have been changed over the years?