Mich. Comp. Laws § 462.11: Special contract rates.

Sec. 11.

Nothing in this act shall be construed to prevent concentration, commodity, transit and other special contract rates, but all such rates shall be open to all shippers for a like kind of traffic under similar circumstances and conditions, and shall be subject to the provisions of this act as to the printing and the filing of the same: Provided, All such rates shall be under the supervision and regulation of the commission.