The Supreme Court has announced it will consider whether public-sector employees are allowed to opt out of unions in a case that could further erode organized labor across the country.

Rebecca Friedrichs is suing the California Teachers Association on the grounds that compulsory union membership violates the principles of free speech and association. Friedrichs v. California Teachers Association will be decided by June, 2016.

Friedrichs wants to opt out of the union on the grounds that her dues are used for political purposes. She can reclaim the 30% of her dues that are used for overt political lobbying, but not the 70% used for negotiation — negotiation that is also political in nature. The California Teachers Association, or CTA, negotiates salaries, pensions, class sizes and tenure — all of which have a political component.

Public-sector unions cannot force government employees to become members but, because all public-sector workers are covered by the same collective-bargaining agreement, employees who opt out still are required to pay agency fees. Agency-fee payers lose some benefits of union membership, such as liability insurance for teachers, but have to pay for all union activities except those that are narrowly defined as political. The line between political and nonpolitical spending is often blurred, leading to constitutional questions over collective bargaining’s violation of the First Amendment.

Public-sector unions are big donors to state governments. In exchange, officials allow unions generous contracts, including lavish pensions. The size of those pensions is one reason why state governments now hold $5 trillion in debt. Friedrichs does not see why her dues should be used to subsidize this travesty.

A win for Friedrichs would be a disaster not only for the California Teachers Association but also for unions such as the SEIU and the American Federation of State, County and Municipal Employees, which receive millions of dollars in additional dues from coerced state government members. Union financial data are difficult to obtain because public-sector unions do not have to file the financial-disclosure forms that are required for private-sector unions.

The headquarters of the California Teachers Association received $186 million in revenue, primarily from program service revenue, for fiscal 2012. For fiscal 2015, member contribution data for all the individual chapters can be estimated since the CTA provides $644 as the average annual dues paid, and the union reports 295,000 members. This would bring the total income from dues to $190 million in 2015. Those funds would be hard to replace. Money is power, power used not only for bosses’ salaries but also for political causes.

According to the Center for Individual Rights, which is representing Friedrichs, the CTA spent over $211 million on politics from 2000 to 2009, including $26 million opposing school vouchers.

The implications of the case are substantial because public-sector employees are the fast-growing sector of union membership. Although the overall union membership rate is steadily declining, reaching 11.1% of wage and salary workers in 2014 from 20.1% in 1983, according to the Labor Department, the decline has been driven by drops in private-sector union membership. Only 6.6% of private-sector employees belonged to unions in 2014. In contrast, 35.7% of public-sector union workers belonged to unions.

If Friedrichs wins, public-sector workers will be able to opt out of joining unions, and it is fair to predict that union membership will decline dramatically. Over 16% of California’s workforce is unionized. In Wisconsin, after Gov. Scott Walker limited collective bargaining for public-sector employees and required annual recertification of unions, union membership declined from 14.2% of the state workforce in 2010 to 11.7% in 2014. In 2014, Wisconsin had 11,000 fewer union members than in 2013.

Those issues all date back to the 1977 Supreme Court case Abood v. Detroit Board of Education. In the 1977 case, collective bargaining was upheld, along with forced dues collection, even if members disagreed with the political ideology of the union leadership. The court’s decision to take up Friedrichs’ case means that Abood is up for review.

The teachers union argues that since Friedrichs and other plaintiffs get the benefits of their negotiations, they should not be allowed to stop paying union dues. But the position taken by the union contradicts other efforts by unions nationwide. Over the past few years, the National Labor Relations Board, or NLRB, has shrunk the size of potential bargaining units. Unions used to have to gain a majority of employees engaged in the same task at the same company — say, mechanics working for Boeing, or retail clerks working for a department store. In 2014, the board allowed unions to organize any subset of employees, as long as they had a “community of interest.” Cosmetic workers at Macy’s, or shoe salesmen at Bergdorf Goodman’s, could vote to be represented by a union without the rest of the store going along.

If small groups of workers can vote to be represented by unions without the rest of workplace voting in favor, why can’t groups of workers vote to leave the union? The NLRB cannot have it both ways. If it is going to let small groups opt in to union representation, it should logically allow other groups to opt out.

No one knows how the Supreme Court will rule next year as Rebecca Friedrichs battles the California Teachers Association. However, the justices’ decision to take the case is no doubt sending a chill up the spine of union leadership.