Union officials in Wisconsin are calling for thousands of ballots to be immediately impounded and recounted following the revelation that a county clerk’s computer error tipped the state Supreme Court election in conservative Justice David Prosser’s favor.

“The mysterious, and arguably timely, discovery of ballots on a personal computer appears to be the latest example of Governor [Scott] Walker and his friends unfairly using the levers of government to silence Wisconsin voters,” Christine Lamitina, a spokeswoman for the Service Employees International Union of Wisconsin, said in a Friday statement.

SEIU has organized a series of protest for later Friday afternoon and is prepared to support legal action, if necessary.

“Following what can only be described as a midnight or sneak attack where Governor Walker summoned his friends to help him eliminate collective bargaining rights for nurses and teachers, this is yet another reminder of the lengths this administration will travel to side with partisan politicians and corporate donors rather than Wisconsinites,” Lamitina said.

The statement is an example of the heightening intensity surrounding the usually sleepy state Supreme Court elections that played out Tuesday and ultimately became a referendum on the Republican governor’s move to curtail collective bargaining rights for state workers.

The latest twist comes from Waukesha County, where County Clerk Kathy Nickolaus held a press conference Thursday night to announce that her initial vote tally omitted more than 14,000 ballots from the Republican stronghold of Brookfield. After they were included in the overall vote totals, a 200-vote lead for the left-leaning challenger, Joanne Kloppenburg, became a 7,500-vote lead for the incumbent, Prosser.

“I’m thankful that this error was caught early in the process. This is not a case of extra ballots being found. This is human error, which I apologize for,” Nickolaus said, according to the Milwaukee Journal Sentinel.

But that was little solace for the unions and liberal activists who poured millions of dollars and countless man-hours into the Supreme Court contest. On the other side, national tea party groups did the same to support Prosser.

“Our members will be mobilizing for 4 p.m. actions at the County Courthouse in Waukesha and the Capitol in Madison, we will continue to mobilize for ongoing actions. We will also be supporting any legal actions and challenges,” SEIU Vice President for Politics and Growth Bruce Colburn said in a statement provided to Roll Call on Friday afternoon.

The Supreme Court contest could decide the balance of power on the state’s high court, on which conservatives now hold a 4-to-3 majority. A Prosser loss would give liberals the majority.

Given the size of Prosser’s current lead — roughly 7,500 votes in a contest that drew 1.5 million ballots — a recount, or a series of legal challenges, is likely.