MADISON, Wis. — Wisconsin’s largest business association has launched a television ad attacking a Democratic state Senate candidate for proposing a gas tax increase even though the group has supported raising the tax for months.

The ad from Wisconsin Manufacturers and Commerce’s political advocacy arm has run since late last month and criticizes Winnebago County Executive Mark Harris for proposing a 3-cent gas tax increase to generate money for road projects in lieu of borrowing. It also urges people to call Harris and tell him that his liberal tax policies are bringing families down.

Harris told Wisconsin Eye, the state’s version of C-SPAN, last month that he wants the tax increase because borrowing will cost the state more in the long run. Harris’ opponent in the 18th Senate District race, Republican Dan Feyen of Fond du Lac, told Wisconsin Eye in July that he would be open to a 5-cent gas tax increase.

A modest gas tax increase was among the things floated on the Wisconsin Manufacturers and Commerce’s website by President Kurt Bauer in December 2014 in lieu of borrowing for roads, as well as raising vehicle registration fees.

“WMC is attacking a Democrat for supporting the same policy that they do, and that his opponent does,” said Scot Ross, executive director of liberal group One Wisconsin Now. “There is no explanation for this dishonesty other than they are more interested in electing Republican politicians than advancing an issue agenda.”

WMC officials had no immediate comment Monday. Harris’ campaign declined comment. Feyen’s campaign didn’t immediately respond to an email seeking comment.

Harris and Feyen’s race is among the most hotly contested in this year’s election. Incumbent Republican Rick Gudex announced last year that he wouldn’t seek re-election, leading Democrats to target the seat as a way to chip into Republicans’ 19-14 majority in the chamber.

Republicans have countered by passing a bill prohibiting county executives from serving simultaneously in the Legislature, a move that would force Harris to trade his $102,800 county job for a $50,950 senator’s salary if he’s elected. Democrats have ripped the law as a direct attack on Harris, who has refused to quit the county position.

The Legislature and Republican Gov. Scott Walker are at odds over how to pay for the rising costs of road construction and maintenance. Walker has refused to raise the gas tax or vehicle registration fees, calling instead for more borrowing and delaying major projects. That stance has created a rift with his fellow Republicans, many of whom call his plan a short-sighted political solution.

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