Which U.S. law of 1913 reintroduced a federal income tax after the 16th Amendment?

The Revenue Act of 1913 reintroduced a federal income tax in the United States after the 16th Amendment was ratified.

Signed by President Woodrow Wilson on October 3, 1913, the law restored federal taxation of personal and corporate incomes. Its individual income-tax rates began at 1% for taxable income above an exemption threshold, with higher rates applying to larger incomes. The measure also substantially reduced tariffs, which had previously supplied much of the federal government’s revenue.

The law followed the Supreme Court’s 1895 decision in Pollock v. Farmers’ Loan & Trust Co., which had invalidated an earlier federal income tax as an unapportioned direct tax. The 16th Amendment removed that constitutional obstacle by authorizing Congress to tax incomes without apportioning the tax among the states. The Revenue Act of 1913 is therefore distinct from the 1861 income-tax law and from the 1909 corporate excise tax.