Rebecca Friedrichs is an Orange County, Calif., math teacher who pays about $700 to her union every year. She didn't sign up for that expense, though. Under California law, she has no choice: Public school teachers either enroll or they don't work.

If she gets her way in court, however, she won't have to pay dues much longer. She is one of 10 educators suing the California Teachers Association to end the dues requirement.

"I just want to have a free choice," she told the Washington Examiner.

Should they get the case to the Supreme Court, a ruling in their favor could effectively make every state a right-to-work state. Big Labor could face huge membership losses as people in previously "closed shop" union workplaces opt out.

The case is being brought by the Center for Individual Rights, a libertarian legal group. CIR President Terry Pell argues that the Supreme Court signaled in last year's Knox v. SEIU ruling that it wants to do this.

"The law presumes that unions represent the interest of all employees. The Supreme Court indicated that this may no longer be the case," he said.

It's a longshot, but Golden State union officials are nevertheless worried. CTA legal director Laura Juran told the Huffington Post it was a "full-frontal assault." The case is currently awaiting a decision on whether it can be expedited to the appeals court level.

California is one of 26 states where unions can negotiate contracts with employers that include "security clauses" - requirements that every worker join or at least pay dues.

This is intended to prevent "free-riding." Since all employees theoretically benefit from the union's negotiating, all should have to pay for it.

But workers are only obligated to pay those bargaining expenses. They can demand refunds of the union's political spending. These are called "Beck" rights, after a 1988 Supreme Court ruling.

Knox v. SEIU put a spotlight on the difficulties faced by workers trying to exercise those rights. The case involved an extra assessment the union put on members to fund a political campaign. They were not given a chance to opt out beforehand.

Though members could eventually get their money refunded, the union in effect got an interest-free loan to advance its political agenda.

Not only did the Supreme Court say unions cannot do that, but Justice Alito wrote in the majority opinion that compulsory union fees "constitute a form of compelled speech and association that imposes a significant impingement on First Amendment rights."

Pell argues that this was a sign from the majority that it would be willing to re-examine the broader issue of whether unions can have security clauses at all. His case echoes that argument.

It also notes Beck rights can be hard to exercise. It's the unions themselves that administrate them. They don't make it easy for workers.

"They don't really explain to you that you have any options. Most teachers are totally unaware they can opt-out of the political portion," Friedrichs said.

Many unions give only a narrow time frame each year -- often just a few weeks -- in which the workers can mail in the opt-out requests.

If they miss that -- or even if the letters just don't dot every "i" and cross every "t" -- the request might be rejected. Workers have to re-do this process every year.

Workers typically only have the union's say-so on what it spending dues money on.

"We don't really know where our money is going," said Harlan Eldritch, another plaintiff in CIR's case. So even workers who are exercising their Beck rights may still be paying for union political activity.

Will such arguments sway the Supreme Court? Pell conceded it is no sure thing.

Then again, as this Supreme Court has shown on cases such as Obamacare and gay marriage, nothing can be taken for granted.