State Police Inspector Gene Adamczyk said eight people were arrested for resisting and obstructing when they tried to push past two troopers guarding the Senate door. He said the troopers used chemical spray after the people refused to obey orders to stop.
The Michigan Senate passed right-to-work legislation, following earlier approval by the House.
The bills would prohibit unions from collecting fees from nonunion workers, which opponents say would weaken organized labor's ability to bargain for good wages while supporters say it would boost jobs.
A measure dealing with private-sector workers passed on a 22-16 vote Thursday after hours of impassioned debate. Four Republicans joined all 12 Democrats in opposition.
Moments after it passed, the Senate passed a bill with similar provisions for government employees. Democrats walked out before the bill was approved on a 22-4 vote.
Union activists repeatedly shouted protests from the gallery and cheered Democrats who denounced the measure.
Gov. Rick Snyder and GOP legislative leaders announced earlier Thursday they would put right-to-work on a fast track.