“This is solely driven by special interests, people who will benefit financially from this,” alleged Sterman, who is part of Missourians for Better Transportation Solutions, a newly formed group in opposition to the referendum. “To me, this is such an egregious example of the abuse of the political system by special interests.”

The proposed sales tax hike would add about 8 cents to a $10 purchase, and would fund a range of transportation-related projects for at least the next 10 years. If approved by the voters, it would go into effect on Jan. 1, and would raise more than half a billion dollars a year.

The Legislature in May approved putting Constitutional Amendment 7 on the ballot, a bipartisan effort that was opposed by Gov. Jay Nixon, a Democrat. He has attacked the proposal as a regressive measure that is especially unfair to the poor — particularly in light of the Legislature’s earlier approval, over Nixon’s veto, of a massive income tax cut that will benefit mostly corporate and wealthy taxpayers.

The sales-tax hike had been expected to go on the November general election ballot but, in a surprise move, Nixon pushed it up to the Aug. 5 primary ballot. That decision threw supporters of the measure for a loop as they were preparing for the coming publicity campaign.