Unions turned out in force to support state workers who are fighting cutbacks in their benefits and bargaining power, as supporters of Republican efforts to scrap the union rights challenged pro-labor protesters face-to-face for the first time.
"The union is the backbone of the middle class. Without the unions, everybody will be serfs and masters," said protester Melanie Hoyle Thompson.
Extra police were put on for security, but the clashes were confined to words. Both sides exchanged chants of "Pass the bill! Pass the bill!" and "Kill the bill! Kill the bill!"
Gov. Scott Walker set off the protests earlier this week by pushing ahead with a measure that would require government workers to contribute more to their health care and pension costs and largely eliminate their collective bargaining rights.
He says the concessions are needed to deal with the state's projected $3.6 billion budget shortfall and to avoid layoffs of government workers.
Democrats have forced the state Assembly to adjourn, so there won't be a vote on the bill until at least Tuesday.
The Associated Press contributed to this story.