CHICAGO (CBS) — A coalition of business, labor, and construction groups has launched a statewide campaign to change the Illinois Constitution to prohibit state government from raiding its road fund whenever it needs to balance the budget.

Supporters called it the “Safe Roads Amendment,” and said it would amend the constitution to put money earmarked for transportation projects in Illinois into a “lockbox” of sorts.

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The measure won overwhelming bipartisan passage in the Illinois General Assembly, and Marc Poulos, executive director of the Illinois, Indiana, Iowa Foundation for Fair Contracting, wants voters to approve the amendment in November.

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“We have had no formal opposition from the governor’s office, or anybody else for that matter. I think everybody recognizes that over the last 12 years, the legislature has diverted or swept nearly $6.4 billion from the transportation fund to use it for other purposes,” he said.

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Poulos said supporters have launched a $1 million ad campaign because the measure needs strong public support to be approved. Any proposed constitutional amendment must be approved by three-fifths of the people voting on the measure, or a majority of those voting in the election in order to be enacted.