[3] Elections to Dáil Éireann, the house of representatives in the Oireachtas, are governed by Article 16 of the Constitution.
[4] In 1959, the Fianna Fáil government of Éamon de Valera put the Third Amendment of the Constitution Bill to a referendum, which proposed to replace the electoral system of proportional representation by means of the single transferable vote (PR-STV) with first-past-the-post (FPTP).
John O'Donovan, a former Fine Gael TD, challenged the Electoral (Amendment) Act 1959, which had been proposed by a previous Fianna Fáil government, on the basis that there were "grave inequalities" with "no relevant circumstances to justify" them.
[5] In O'Donovan v. Attorney-General (1961), Gardner Budd held for the High Court that the Act was unconstitutional.
The court, interpreting the "so far as it is practicable" condition of the Constitution, suggested a 5% variation as the limit without exceptional circumstances.