in U.S. history, series of four acts passed by Republican Reconstruction supporters in the Congress between May 31, 1870, and March 1, 1875, to protect the constitutional rights guaranteed to blacks by the Fourteenth and Fifteenth Amendments.

The major provisions of the acts authorized federal authorities to enforce penalties upon anyone interfering with the registration, voting, officeholding, or jury service of blacks; provided for federal election supervisors; and empowered the president to use military forces to make summary arrests. Under the act of April 20, 1871, nine South Carolina counties were placed under martial law in October 1871. This act and earlier statutes resulted in more than 5,000 indictments and 1,250 convictions throughout the South (South, the). In subsequent Supreme Court decisions, various sections of the acts were declared unconstitutional.