Mackinac Island — The November general election might end up being a referendum on Michigan’s powerhouse corporate donors.

A voter-initiated proposal seeking to ban political donations from DTE Energy, Consumers Energy and state contractors like Blue Cross Blue Shield of Michigan has a shot at making the November ballot. The bid is putting this nonautomotive Big Three on defense for their prolific giving to Michigan politicians through official campaigns, leadership political action committees and the slushier dark money variety — known as 501(c)4 accounts — that have become commonplace at the state Capitol.

As the state’s political elites meet this week on Mackinac Island for the annual Mackinac Policy Conference for time-honored gabbing, seersucker suits and parties, a grassroots coalition is getting out the mop in Lansing.

The ballot campaign committee, Michiganders for Money Out of Politics, known as the “MMOP” campaign, said it turned in more than 562,000 signatures on Wednesday, the deadline to submit petitions for ballot questions to make the November ballot. Legal challenges notwithstanding, the group needs 356,958 valid petition signatures to qualify for a spot on the Nov. 4 ballot.

The proposal is, in effect, a declaration of war on traceable and untraceable money that permeates throughout Michigan politics — the kind that underwrites this week’s confab at the Grand Hotel and assorted haunts on an island without cars.