About 300 people gathered Thursday to protest the passage of a right-to-work bill, a Wisconsin Capitol Police official said.
Union members and others joined together outside the Capitol as the state Assembly prepared to debate the measure through the night and into early Friday morning.
Speakers at the rally said they are not giving up because too much is at stake. AFL-CIO official Stephanie Bloomingdale called the bill a "sneak attack" on unions that skirts democracy and justice.
The Senate passed the measure last week. Once it clears the Assembly it will head to Gov. Scott Walker, who has said he will sign it Monday.
The protest was smaller than ones last week and Saturday that attracted a couple thousand people, based on police estimates.
Democrats argue right-to-work would be bad for workers, wasn't wanted by businesses and would hurt the state's economy. Republican supporters maintain the law will give workers the freedom to decide whether to pay union dues and will attract more business to the state.