Mich. Comp. Laws § 168.600

Sec. 600. At the 1964 fall congressional district convention provided for in this act for congressional districts, the majority of the electors of which, reside in a county having a population of over 1,500,000, and at a caucus of each other congressional district held at the time of the 1964 fall state convention, there shall also be elected for each political party a congressional district chairperson, a vice-chairperson of the opposite sex of the chairperson, a secretary, a treasurer, and a committee of 15 members to serve for 2-year terms or until their successors are duly elected and qualified. Thereafter, beginning in 1967, the elections shall be held at the spring congressional district conventions and the caucuses held at the time of the spring state convention in every odd numbered year.