LANSING, Mich. — A right-to-work law may be on the books in Michigan, which has the nation’s seventh-highest percentage of unionized workers. But those considering opting out of paying dues or fees will have to wait months — in some cases, years — to do so.

Michigan, a mainstay of organized labor despite thinning union ranks, is the 24th right-to-work state. Because the law applies to labor contracts that are extended or renewed starting Thursday, many employees will not be affected until their existing collective bargaining agreements end.

“I’ve got a long way to go until I can exercise my right,” said Terry Bowman, 47, who works on the line at a Ford Motor plant in Ypsilanti. Contracts between unions and Detroit automakers are effective until September 2015.

Bowman, who founded a group called Union Conservatives, said he is leaning toward ending his membership in the United Auto Workers — of which he has been a member since 1996 — unless it drops its “political agenda.” He said there are many more blue-collar people like him, but they are scared to publicly support right-to-work because of pressure from union leaders after the law won quick approval in December from the GOP-led Legislature and Republican Gov. Rick Snyder.

Though Bowman does not expect a “mass exodus,” he said some unions could lose a quarter of their membership.

Neighboring Indiana enacted a right-to-work law in February 2012. The early results: Union membership declined to 9.1 percent of the workforce last year from 11.3 percent in 2011, according to federal statistics — a loss of 56,000 people. Most of Indiana’s unions have not yet seen a big drop-off in membership, but many contracts are still in place from before the law took effect.