Michigan's House passed a right-to-work bill Tuesday for public-sector workers, and the legislation was headed to Republican Gov. Rick Snyder's desk.
The state House voted 58-51 to pass House Bill 4003, one of two right-to-work bills. The Lansing State Journal said the state House would next take up Senate Bill 116, which would affect private-sector employees.
All Democrats and some Republicans opposed the state House bill, but the State Journal said both of the right-to-work bills were expected to pass because of the 64-46 Republican majority in the state House.
Democrats were tried to impede the vote on the private sector bill with amendments, which were quickly rejected.
The legislation would block requirements forcing workers to pay union fees as a condition of employment.
Outside the Capitol, a crowd of protesters swelled to 10,000, as demonstrators pounded drums and emptied buckets, The Detroit News reported.
A large pro-union rally was held in front of Lansing's City Hall and giant loudspeakers broadcast speeches across the Capitol lawn, the report said.
United Auto Workers President Bob King was among the speakers.
"Unions built the middle class of America. This is a national attack," he said. "These folks want to shift more and more of the wealth to a smaller and smaller group of people."
The News said the speakers included firefighters, teachers and factory workers, who promised Tuesday's protest was just the start, and said they would follow legislators all over the state to remind the public of legislators' votes.
The Capitol was closed after officials said the building had reached its capacity, leaving thousands of union members on the lawn outside, The New York Times reported.
Streets around the Capitol were closed to traffic, the Times said, while state police, some carrying riot gear, stood guard throughout the building and along nearby streets.
Protesters began arriving as early as 5 a.m. carrying supplies to help them stay warm during a day that started with chilly 22-degree weather, the News reported.
Unions fear the legislation could undermine their political presence, their membership numbers and their clout. They also fear a drop in wages.
Three school districts closed for the day as too many teachers had called in sick to attend the rally to keep classrooms staffed.
"We're encouraging our members to stand in solidarity as a show of anger, defiance and frustration for this whole Legislature," Detroit Federation of Teachers President Keith Johnson said.
"It is only designed to break unions and has noting to do with workers," he said.
"They're trying to destroy public schools and close down public services, which are the backbone of the state," said teacher Steve Conn at Cass Tech High School.
Advocates of right-to-work say it gives employees and employers more freedom.