Business M-28 (Bus. M-28) is a state trunkline highway serving as a business route that runs for through the downtown districts of Ishpeming and Negaunee in the US state of Michigan. The trunkline provides a marked route for traffic diverting from U.S. Highway 41 (US 41) and M-28 through the two historic iron-mining communities. It is one of three business loops for M-numbered highways in the state of Michigan. There have previously been two other Bus. M-28 designations for highways in Newberry and Marquette.