Article 16 of the Constitution dealing with the electoral system says "Dail Eireann shall be composed of members who represent constituencies determined by law."

It states that "the number of members shall from time to time be fixed by law, but the total number of members of Dail Eireann shall not be fixed at less than one member for each thirty thousand of the population, or at more than one member for each twenty thousand of the population".

The Constitution determines that TDs "shall be elected by the system of proportional representation by means of the single transferable vote".

It also forbids the enactment of any legislation "whereby the number of members to be returned for any constituency shall be less than three".