Mich. Comp. Laws § 168.132

Sec. 132. A general primary election of all political parties shall be held in every election precinct in this state on the Tuesday succeeding the first Monday in August preceding every general November election, at which time the qualified and registered electors of each political party within every congressional district shall vote for party candidates for the office of representative in congress to be filled at said election: Provided, That this section shall not apply to parties required to nominate candidates at caucuses or conventions.