Michigan Compiled Laws, Chapter 462. Railroads § 462.11

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.