poll tax, a capital tax levied equally on every adult in the community. Although no longer a significant source of revenue for any major country, the poll tax did provide large sums for many governments until well into the 1800s. The tax has long been attacked as being an unfair burden upon those less able to pay. In the United States, the poll tax has been connected with voting rights. Poll taxes enacted in Southern states between 1889 and 1910 had the effect of disenfranchising many blacks as well as poor whites, because payment of the tax was a prerequisite for voting. By the 1940s some of these taxes had been abolished, and in 1964 the 24th Amendment to the U.S. Constitution disallowed the poll tax as a prerequisite for voting in federal elections. In 1966 this prohibition was extended to all elections by the U.S. Supreme Court, which ruled that such a tax violated the "equal protection" clause of the 14th Amendment to the Constitution. In 1990, Prime Minister Margaret Thatcher of Great Britain introduced a poll tax with exemptions for people with low incomes or disabilities. The measure was extremely unpopular and played a role in her replacement as prime minister later that year.