WASHINGTON (AP) -- The largest teachers union in Michigan still represents Jason LaPorte at the bargaining table, but he no longer pays anything to support the union.
LaPorte and thousands of other public school teachers stopped contributing to the union after the state's new right-to-work law took effect in 2013. Membership in the Michigan Education Association has since dropped by 19 percent.
A similar fate could soon be in store for public-employee unions around the country as the Supreme Court considers whether government workers who choose not to join a union can be required to nevertheless pay fees that cover collective bargaining.
The high court hears arguments Monday in a California case brought by a group of public school teachers who claim such mandatory fees violate the First Amendment rights of workers who disagree with the union's positions.
Unions fear the potential loss of tens of millions of dollars in fees could reduce their power to bargain for higher wages and benefits for teachers, firefighters, sanitation workers and other government employees.
While half the states already have right-to-work laws banning mandatory fees, most members of public-employee unions are concentrated in more liberal-leaning states that don't, including California, New York and Illinois.
The lead plaintiff in the case is Rebecca Friedrichs, a public school teacher in Orange County, California, who says she left the California Teachers Association after becoming disillusioned with its mission. She wants the high court to overturn a 39-year-old ruling that said states can require non-members to pay "fair share" fees. These fees cover what it costs the union to represent them in bargaining as long as the money doesn't go for political purposes.
That 1977 case, which involved a group of Detroit schoolteachers, said the fee system prevents non-members from "free riding," since the union still has a legal duty to represent all workers. The high court has raised doubts about the viability of the ruling in two recent cases, but has stopped short of overturning it.
Opponents of the fee system want the justices to essentially convert those more liberal states into de-facto right-to-work states for public employee unions, where workers still covered by the union can pay nothing at all.
In Michigan, a historic labor stronghold, the loss of revenue at the MEA has led to cuts in staff and more time spent urging members not to leave, said spokesman Doug Pratt. That means fewer resources for bargaining contracts or efforts to reduce class size, curb standardized tests and increase school funding.
"It undermines our ability not only to bargain, but to operate as a collective," Pratt said. "It's about strength in numbers."
While it may be too early to tell whether Michigan's law has had an impact on the bargaining process, Pratt said it has encouraged union officials to spend more time reminding members what the union does for them.
The challengers in California say it's impossible to separate politics from the bread-and-butter workplace issues on which unions spend money.
"It is difficult to imagine more politically charged issues than how much money local governments should devote to public employees, or what policies public schools should adopt to best educate children," their lawyers said in a brief to the court.
For LaPorte, a Saginaw schoolteacher for 11 years, his decision to give up his union membership wasn't about politics, but frustration over an agreement that led to a pay freeze for younger teachers. He's involved in a separate lawsuit brought by the Mackinac Center, a conservative Michigan think tank, challenging the union's policy of giving workers only a one-month window each year to opt out of fees.
"If the union wants membership, then they need to offer a better product," LaPorte said.
But union advocates say the Supreme Court case is all about politics — that conservative groups aim to weaken labor unions that tend to overwhelmingly support Democratic candidates and policies.
The case also threatens to unravel thousands of contracts around the country that were negotiated relying on the four-decade old system, said Lily Eskelsen Garcia, president of the National Education Association, the nation's largest teachers union. Those agreements help promote efficiency and avoid costly disruptions, union officials say.
The challengers are backed by the same groups that supported Wisconsin Gov. Scott Walker's effort to take away most collective bargaining for public employees. The action has left Wisconsin's public unions reeling from membership declines of up to 70 percent.
Roughly half of all union members are government workers. About 36 percent of public-sector employees are in a union, compared to just 6.6 percent of private-sector workers.
"Since private-sector unionism hardly exists, they are now attacking public-sector unions," said Nelson Lichtenstein, a labor professor at the University of California-Santa Barbara. "Unions will be weakened as bargaining and political institutions."
In Michigan, the Koch brothers-backed group Americans for Prosperity bought a full-page ad in the Detroit Free Press in 2014 with a form that teachers could send to their union to drop out. The Mackinac Center mailed post cards reminding union members about deadlines to withdraw.
Overall, Michigan's union membership fell from 16.3 percent to 14.5 percent in 2014, the first full year under the right-to-work law.
Vincent Vernuccio, director of labor policy for the Mackinac Center, said unions have to prove their worth to members and "can no longer take those dues or fees for granted."