Mich. Comp. Laws § 752.543: Unlawful assembly.

Sec. 3.

It is unlawful and constitutes an unlawful assembly for a person to assemble or act in concert with 4 or more persons for the purpose of engaging in conduct constituting the crime of riot, or to be present at an assembly that either has or develops such a purpose and to remain thereat with intent to advance such purpose.