Mich. Comp. Laws § 168.603a

Sec. 603a. In counties having a population of more than 400,000 persons, all members of the state legislature shall be members of the congressional district committee of their party in each congressional district which encompasses their legislative district in whole or part, and shall serve in addition to the committee of 15 members prescribed in section 600 of this act. Such legislators shall also be seated as delegates-at-large to all congressional district conventions of their party held during their term of office in congressional districts which encompass their legislative district in whole or part. As congressional district committee members and as delegates-at-large, they shall have a voice and vote.