Opponents of so-called right-to-work measures say they drain unions of money and weaken their ability to bargain for good wages and benefits. Supporters insist it would boost the economy and job creation.
A victory in Michigan would give the movement its strongest foothold yet in the Rust Belt region, where organized labor already has suffered several body blows.
But even before the votes, protesters streamed inside preparing for what appeared inevitable after Gov. Rick Snyder joined GOP legislative leaders Thursday morning in announcing they would push swift passage.
"This is all about taking care of the hard-working workers in Michigan, being pro-worker and giving them freedom to make choices," Snyder said during a news conference with House Speaker Jase Bolger and Senate Minority Leader Randy Richardville.
"The goal isn't to divide Michigan, it is to bring Michigan together," Snyder said.
Lt. Gov. Brian Calley repeatedly gaveled for order as Democratic senators denounced the legislation to applause from protesters in the galley. At one point, a man shouted, "Heil Hitler! Heil Hitler! That's what you people are." He was quickly escorted out. Another later yelled, "We will remember in November."
Eight people were arrested for resisting and obstructing when they tried to push past two troopers guarding the Senate door, state police Inspector Gene Adamczyk said.
The Capitol, which was temporarily closed because of safety concerns, reopened Thursday afternoon, sending hundreds of protesters streaming back inside with chants of, "Whose house? Our house!" Adamczyk said a judge ordered the building reopened.
But the decision to push forward in the waning days of the Legislature's lame-duck session infuriated outnumbered Democrats, who resorted to parliamentary maneuvers to slow action but were powerless to block the bills that were expected to be introduced Thursday.
Protesters waved placards and chanted slogans such as "Union buster" and "Right-to-work has got to go." Adamczyk said the troopers used pepper spray after the people refused to obey orders to stop.
He estimated that about 2,500 visitors were inside the Capitol, where their shouts reverberated off stone halls and frequently could be heard inside the ornate chambers.
After repeatedly insisting during his first two years in office that right-to-work was not on his agenda, Snyder reversed course Thursday, a month after voters defeated a ballot initiative that would have barred such measures under the state constitution.
In an interview with The Associated Press, Snyder said he had kept the issue at arm's length while pursuing other programs to bolster the state economy. But he said circumstances had pushed the matter to the forefront.
"It is a divisive issue," he acknowledged. "But it was already being divisive over the past few weeks, so let's get this resolved. Let's reach a conclusion that's in the best interests of all."
Also influencing his decision, he said, were reports that some 90 companies had decided to locate in Indiana since that state adopted right-to-work legislation. "That's thousands of jobs, and we want to have that kind of success in Michigan," he said.
Snyder and the GOP leaders insisted the legislation was not meant to weaken unions or collective bargaining, saying it would make unions more responsive to their members.
Senate Democratic leader Gretchen Whitmer said she was "livid."
"These guys have lied to us all along the way," she said. "They are pushing through the most divisive legislation they could come up with in the dark of night, at the end of a lame-duck session and then they're going to hightail it out of town. It's cowardly."
Republicans have commanding majorities in both chambers — 64-46 in the House and 26-12 in the Senate. Under their rules, only a simple majority of members elected and serving must be present to have a quorum and conduct business. For that reason, Democrats acknowledged that boycotting sessions and going into hiding, as some lawmakers in neighboring Indiana and Wisconsin have done in recent years to stall legislation unpopular with unions, would be futile in Michigan.
Throngs of protesters spent weeks outside capitol buildings in those states, clashing over union rights.
"We will not have another Wisconsin in Michigan," Adamczyk said. "People are allowed to protest, but they need to do in a peaceful manner."