A proposed Dane County Regional Transit Authority wouldn’t be able to impose a new sales tax to fund buses, commuter rail and road improvements without voter approval under a proposal to be included in the Senate version of the 2009-11 budget plan and supported by area officials.

 Madison Mayor Dave Cieslewicz, Middleton Mayor Kurt Sonnentag and Dane County Executive Kathleen Falk all support the measure state Sen. Jon Erpenbach, D-Waunakee, urged his Democratic colleagues in the Senate to adopt.

"From our point of view, whether it’s binding in the legislation or not, it’s politically binding on us," Cieslewicz said.

The spending plan approved by the Assembly last week authorizes the creation of an RTA for the Madison area. It would be allowed to levy a sales tax of up to 0.5 percent after voters are asked their opinions about it in an advisory referendum.

But Erpenbach said Tuesday Senate Democrats agreed in private to authorize the RTA but make the referendum binding — giving voters final say over any potential tax increase.

"The way for this to be successful is to get a majority of people behind what you want to do," he said.

The proposal will be added to the two-year spending plan the Senate is scheduled to debate today, Erpenbach said. If the full Senate approves it, the differences between the Assembly and Senate versions would have to be worked out.

Senate Democrats also agreed to let the Dane County authority spend money it raises on roads, a measure the Assembly included in its budget.

The transit authority proposal is controversial, and some opponents have argued that it could raise taxes without being accountable to voters.

Eileen Bruskewitz, a Dane County supervisor who opposes the RTA, said making the referendum binding is "the right thing to do. It’s the fair thing to do."

Senate Majority Leader Russ Decker, D-Weston, said Monday he thinks all local transit authorities should be subject to binding referenda before taxing. Sen. Fred Risser, D-Madison, said he supported the binding referendum language proposed by Erpenbach. Sen. Mark Miller, D-Monona and co-chairman of the Legislature’s budget committee, wouldn’t comment on the proposal. Becky Sweeney, a spokeswoman for Assembly Speaker Mike Sheridan, D-Janesville, said she couldn’t comment on the proposal until the Senate approves final language.

— Reporter Jason Stein contributed to this story.