The 16th Amendment to the Constitution of the United States is important because it establishes the right of Congress to levy income taxes. The amendment was ratified in February of 1913.
Prior to the amendment, the primary source of federal revenue was custom duties and excise taxes. In prior years, when an income tax was proposed, it was only temporary and done during emergency situations, such as the Civil War.
Connecticut, Utah, New Hampshire and Rhode Island all rejected the proposal to ratify the amendment. Florida and Pennsylvania chose not to consider the amendment. The remaining states all voted in favor of the amendment.