The law could hamper union efforts to organize new factories and other employers, said Kristin Dziczek, head of the labor and industry group at the Center for Automotive Research in Ann Arbor. Auto-parts manufacturers, which generally pay lower wages than the big vehicle-manufacturing companies such as GM and Ford, might see union membership decline.
Legal challenges could raise more questions about the measures' long-term impact. One such issue arose Wednesday as a member of the Michigan Civil Service Commission said the Legislature had no authority to impose right-to-work policies on most state government workers.
The state constitution puts the commission in charge of such matters, said Robert Swanson, one of four members of the panel, who are appointed by the governor. A spokeswoman for Snyder disagreed, insisting the laws apply to all public employees.
The right-to-work law already exempts police and firefighters because they are covered by an existing law requiring that their labor disputes be settled through binding arbitration.
Peer pressure and tradition may go a long way to keep larger, more established unions intact. The United Auto Workers, for example, has been intertwined in Michigan's tight culture of manufacturing cars and trucks for 77 years.
At most auto plants, the union does more than just bargain for wages. It's a brotherhood that holds social and charitable events at union halls and organizes motorcycle rides and bus trips to baseball games and amusement parks. The halls are also sites for weddings and other celebrations, and where retirees gather to talk about old times. Simply put, a worker who shuns the union could be ostracized.
For those reasons, the UAW has seen only a few people opt out of joining the union at GM factories, even in states that have had right-to-work laws for a long time.
At GM's factory in Spring Hill, Tenn., only eight of the 1,650 blue-collar workers have rejected union membership. GM has hired more than 220 new workers at the plant and all have joined, UAW spokeswoman Michele Martin said.
Fewer than a dozen of the 3,200 workers at a huge GM SUV plant in Arlington, Texas, haven't joined, said Mike Cartwright, president of UAW Local 276.
"No one wants to be a free rider," said Cartwright, who helps to sell the union to every new worker at the factory that opened in 1954. "We do a pretty good job of explaining the big picture. It doesn't hurt the company. We support the company."
If anything, the right-to-work fight has boosted members' appreciation of their unions, said George McGregor, president of UAW Local 22 in Detroit.
"This is the best organizing tool that we will ever have," McGregor said.
Associated Press writers Tom Krisher in Detroit, Tom LoBianco in Indianapolis and Todd Richmond in Lansing contributed to this story.