Election Day in Wisconsin, Tuesday, is becoming yet another chapter in the ongoing debate over the collective-bargaining power for unions in that state. Both political parties are targeting an open state Supreme Court seat with the hope that it will swing the majority vote on the issue in their favor – a prospect that has elevated the race to the national stage and is generating millions of dollars from national interest groups.

The stakes are high because both sides agree that whoever wins will probably end up ruling on the controversial union bill, which strips collective-bargaining rights from public-employee unions. That legislation is expected to wind its way through the state court system in the coming weeks. On Friday, a circuit court judge ruled that the temporary restraining order designed to block the legislation will stand for at least two months in order to determine whether Republican legislators violated the state’s open meeting policy in making it law. The administration of Gov. Scott Walker (R) insists the law’s passage was sound and is already adopting it as official policy.

Tuesday’s election is being seen as giving voters their first opportunity to weigh in on the matter. Republicans favor Justice David Prosser, the incumbent since 1998, while Democrats and union organizations are backing Wisconsin Assistant Attorney General JoAnne Kloppenburg.

IN PICTURES: Wisconsin protest signs

In a different year, the race would be unencumbered by outside issues, says Mike McCabe, executive director of the Wisconsin Democracy Campaign, a nonprofit watchdog group located in Madison, the state capital. But then came the fight over Governor Walker’s bill, which critics say erodes union power in that state but supporters say is needed to shore up the state budget and deal with the big deficit.

“I don’t think there’s any question that [the Supreme Court election] is a referendum on Scott Walker,” Mr. McCabe says. “We’re not used to having Wisconsin Supreme Court elections get national attention. They don’t even have attention in the state.”

Tuesday’s election, McCabe adds, is being seen as an extension of the citizen protests that took place outside the State Capitol starting in mid-February. As 14 state Democrats camped in Illinois to prevent their Republican peers from achieving the quorum needed to pass the bill, Madison streets were filled for weeks with hundreds of thousands of protesters and national media.

Interest from outside Wisconsin

“Because of what happened there in the last month and a half, [the election] is giving the electorate the first opportunity to express their opinion via the ballot box ... and I think people are seizing the opportunity,” McCabe says.

The election’s outcome is seen as so pivotal that national special-interest organizations from outside the state are getting involved. According to data compiled by the Brennan Center for Justice at New York University School of Law, a nonpartisan public-policy organization, spending on television advertising for the election reached $1.4 million by March 27 – and special-interest groups accounted for 82 percent of the spending. By comparison, during the last state Supreme Court election in 2009, special-interest groups were responsible for just 23 percent of all spending for television advertising.

For the current election, both candidates were provided $100,000 in public money during the primary and $300,000 for the general election. But the greatest increase in spending for television advertising was expected to take place last week. By Tuesday, McCabe estimates, the combined spending for both sides will total almost $5 million.

Among the biggest spenders, according to data compiled through March 27, are the Greater Wisconsin Committee, a liberal organization that spent more than $575,000, and the Wisconsin Club for Growth, which spent about $415,000.

Sarah Palin weighs in

The Tea Party Express, a national political-action committee (PAC), has spent more than $150,000 on television advertising so far disparaging Ms. Kloppenburg. Sal Russo, whose firm operates the PAC, told Politico that his organization became involved “because the left wants to use success in Wisconsin as a warning to fiscal conservatives in other states.”

Sarah Palin also weighed in this week, tweeting to followers to vote for Justice Prosser and to visit his website.

The heightened attention is expected to result in greater voter turnout, especially in Dane and Milwaukee counties, which are the most populated and most Democratic counties in the state. The Wisconsin Government Accountability Board is predicting a 20 percent voter turnout, although local experts say it will be higher.

Whatever the outcome, a resolution over the collective-bargaining law is not guaranteed. John McAdams, who teaches political science at Marquette University in Milwaukee, says the issue “will be a battle” once it reaches the state Supreme Court because of the variety of challenges to the law. Some argue its passage violated procedural law, while others say it is constitutionally flawed.

“Pretty much everything will be litigated,” he says. “This whole business is an invitation to prolonged trench warfare.”

IN PICTURES: Wisconsin protest signs