Compiled Laws, Chapter 168. Michigan Election Law § 168.259

Sec. 259. When a candidate of any political party has filed nominating petitions or filing fee for such office and has been nominated for said office by said party, he shall not be permitted to withdraw unless he has removed from the county, or has become physically unfit. No vacancy shall be filled by the county committee except for the causes and as herein specified: Provided, That this prohibition shall not be construed to prohibit the withdrawal of any candidate who has been nominated without having filed a nominating petition or filing fee, and whose name has been written or placed on the ballot of any political party.