The move potentially complicates chances for completing the deal just as its prospects seemed to be improving.
The organization is contacting 90,000 conservatives in Michigan and encouraging them to rally against a plan to provide $195 million in state money to help settle Detroit pension holders' claims in the case and prevent the sale of city-owned art.
The group could run ads against members of the Republican-controlled Legislature who back the appropriation, which has been proposed by Republican Gov. Rick Snyder. The group says giving more public money to Detroit is a waste.
Snyder proposed the cash to help bring the 10-month-long bankruptcy case to a conclusion.