(1) Following the decennial census of 1990 and in each legislature thereafter, the senate shall consist of not less than thirty nor more than thirty-five members. The legislature may fix the number of members of the house of representatives at not more than two times as many representatives as there are senators. The senators and representatives shall be chosen by the electors of the respective counties or districts into which the state may, from time to time, be divided by law.
(2) Whenever there is reason to reapportion the legislature or to provide for new congressional district boundaries in the state, or both, because of a new federal census or because of a decision of a court of competent jurisdiction, a commission for reapportionment shall be formed on order of the secretary of state. The commission shall be composed of six members. The leaders of the two largest political parties of each house of the legislature shall each designate one member and the state chairmen of the two largest political parties, determined by the vote cast for governor in the last gubernatorial election, shall each designate one member. In the event any appointing authority does not select the members within fifteen calendar days following the secretary of state's order to form the commission, such members shall be appointed by the Supreme Court. No member of the commission may be an elected or appointed official in the state of Idaho at the time of designation or selection.
(3) The legislature shall enact laws providing for the implementation of the provisions of this section, including terms of commission members, the method of filling vacancies on the commission, additional qualifications for commissioners and additional standards to govern the commission. The legislature shall appropriate funds to enable the commission to carry out its duties.
(4) Within ninety days after the commission has been organized or the necessary census data are available, whichever is later, the commission shall file a proposed plan for apportioning the senate and house of representatives of the legislature with the office of the secretary of state. At the same time, and with the same effect, the commission shall prepare and file a plan for congressional districts. Any final action of the commission on a proposed plan shall be approved by a vote of two-thirds of the members of the commission. All deliberations of the commission shall be open to the public.
(5) The legislative districts created by the commission shall be in effect for all elections held after the plan is filed and until a new plan is required and filed, unless amended by court order. The Supreme Court shall have original jurisdiction over actions involving challenges to legislative apportionment.
(6) A member of the commission shall be precluded from serving in either house of the legislature for five years following such member's service on the commission.