Also, as Snyder noted, fewer than 20 percent of Michigan workers are union members. Organized labor rolls and influence have declined in recent years, emboldening Republicans to challenge unions even in their historic Rust Belt stronghold.
Wisconsin Gov. Scott Walker survived a recall attempt after curtailing collective bargaining for most public employees. After Indiana enacted a right-to-work law this year, voters in November gave Republicans a legislative majority so large they can conduct business without any Democrats present. Snyder and GOP lawmakers already had chipped away at Michigan union rights, even forbidding school districts from deducting dues from teachers' paychecks.
Another problem for opponents: Right-to-work has considerable voter support. A statewide phone survey of 600 likely voters conducted in late November by the Lansing firm EPIC-MRA found 54 percent favored the idea while just 40 percent opposed it, although they were evenly divided when asked whether Michigan should become the 24th state with such laws. The margin of error was plus or minus 4 percentage points.
Senate Majority Floor Leader Arlan Meekhof, straining to be heard over jeering opponents in the chamber's gallery, argued last week that by enacting right-to-work, "we are announcing to the world that we are moving Michigan forward. We are for workplace fairness and equality and we are for job creation."
To go up against all those obstacles, unions and Democrats will need solid organization, steadfastness and a persuasive case.
Democratic U.S. Rep. Sander Levin, who as a state legislator in the 1960s sponsored the labor law that right-to-work measures would overturn, called for a "massive education campaign" to remind voters of unions' role in building the middle class and explain how the new policy will weaken their ability to bargain for good wages and benefits.
"What's at stake is the cooperative, constructive labor-management relations that have ripened over the last 15 to 20 years," Levin said. "This governor is essentially saying that instead of collaboration, it's going to be dog-eat-dog."
Michigan Education Association President Steve Cook said Republicans pushed the one issue guaranteed to unite an often fractious labor movement.
Activists have filed a lawsuit claiming the state Open Meetings Act was violated when police temporarily barred doors to the Capitol during last week's debate. Other legal challenges are being considered, opponents said. Union members distributed leaflets Saturday at a college basketball game in the Upper Peninsula city of Marquette.
That's only the beginning, Cook said. While declining to discuss specific plans, he vowed labor would fight hard to unseat right-to-work supporters in 2014 and might try to recall some legislators even earlier.
"Whoever votes for this," Cook said, "is not going to have any peace for the next two years."
Associated Press writer Ed White contributed to this report from Detroit.