They'll be deciding whether to recall their Republican governor, Scott Walker and replace him with Democrat Tom Barrett.
A victory by the first-term governor could give Republicans a major boost in efforts to make Wisconsin a battleground state in the November presidential election.
Tom Foreman reports.
The movement to boot Governor Scott Walker started when he outraged union members and their supporters in early 2011.
He said his legislation to reduce collective bargaining rights for state employees was needed to balance the budget. But democrats called it a sneak attack on working families.
They've gathered hundreds of thousands of signatures all across WIsconsin as the divisive recall campaign thunders to a conclusion.
As the race has intensified between walker and his democratic challenger, Milwaukee mayor Tom Barrett, so have the nasty ads and the bitter words. "I call them union pigs! They root in madison like pigs root in pig sties!"
That widening fight has drawn big money, and big names from outside the state. As national republican and democratic forces push for a win.
on both sides, activists clearly see this race as a referendum on fiscal policies, on liberal versus conservative political philosophies, and of how Wisconsin may lean in the presidential race.
Each candidate has denounced the ugliness of the race. But they've also attacked each other ferociously.
so however things turn out, it seems unlikely the fight will be gone with a win.
Tom Foreman, CNN, Washington.