The Electoral (Amendment) Act 1959 (No. 33) was a law in Ireland which sought to revise Dáil constituencies. It was found to be repugnant to the Constitution and never came into effect.
It was challenged by John O'Donovan, a Fine Gael senator and former TD. In O'Donovan v. Attorney-General (1961), the High Court held that the Act was unconstitutional and suggested that the ratio of representation to population across constituencies should differ by no more than 5%. The court, interpreting the "so far as it is practicable" condition of the Constitution, suggested a 5% variation as the limit without exceptional circumstances.
It was formally repealed by the Electoral (Amendment) Act 1961.