WASHINGTON -- The American Federation of State, County and Municipal Employees (AFSCME) is ostensibly a public worker union. In truth, it is nothing more than an appendage of the Democratic Party. One hundred percent of its political contributions go to Democrats, and it works tirelessly to increase government spending and stop Republicans who want to reform state government.

Should AFSCME be able to force public workers who disagree with its liberal agenda to pay union dues and support it? That was the question before the Supreme Court this week, when justices heard oral arguments in Janus v. AFSCME, a case brought by Illinois child-support specialist Mark Janus, who argues that forcing him to contribute to union coffers violates his First Amendment rights by compelling him to support speech with which he disagrees.

Public worker unions cannot compel nonmembers to directly pay for political activities, but in states that have not passed "right to work" laws, they can force public employees to pay an "agency fee" to support the union's collective bargaining efforts. Of course, the union gets to decide what spending is political, and the fees are usually between 80 and 100 percent of union dues. Moreover, to stop paying for the union's political activities, workers must proactively object -- and then get a partial refund of what the union claims is the extent of its political spending.

This is a scam. The unions know that if they cannot compel workers to pay union dues, most will choose not to do so. In Indiana, when then-Gov. Mitch Daniels (R) signed a "paycheck protection" law barring forced collection of union dues, only 5 percent of state employees chose to continue paying -- and public worker union membership dropped from 16,408 in 2005 to just 1,490 in 2011. In Wisconsin, when Gov. Scott Walker (R) passed Act 10, which included paycheck protection, AFSCME membership fell by more than half -- from 62,818 in 2011 to 28,745 the following year. Other public worker unions faced similar losses in membership. And those losses have been sustained. According to a Milwaukee Journal Sentinel analysis, by 2016 Wisconsin had "132,000 fewer union members, mostly teachers and other public workers -- enough to fill Lambeau Field and Miller Park, with thousands more tailgating outside." (Disclosure: I have co- written a book with Walker.)

Apparently, when you don't force workers to stay in a union, many choose to leave.

Janus wants the same freedom to choose. He argues that all spending by public-sector unions is political spending. Chief Justice John G. Roberts Jr. seemed sympathetic to this type of argument in a similar case that deadlocked two years ago after the death of Justice Antonin Scalia, noting that even negotiations over wages affect the state budget. "The amount of money that's going to be allocated to public education as opposed to public housing, welfare benefits, that's always a public policy issue," he said.

Justice Anthony M. Kennedy got to the heart of the matter this week, when he asked AFSCME lawyer David Frederick, "If you do not prevail in this case, the unions will have less political influence?" Frederick admitted they would. "Isn't that the end of this case?" Kennedy asked. Yes, it is. As Kennedy put it, the question before the court is whether states can "mandate people that object to certain union policies to pay for the implementation of those policies against their First Amendment interests."

Liberals say conservatives are trying to use the court to break the power of public-sector unions. But if the only way they can maintain their political power is through coercion, then they don't deserve that power in the first place. The reason so many workers quit when given the chance is because they know the unions use their power not to benefit workers but to enrich themselves. In Wisconsin, the teachers unions used collective bargaining to force school districts to buy health plans from union-affiliated insurers at inflated prices, when they could have gotten much cheaper insurance on the open market. Once the unions' coercive power was broken and school districts were able to open their health insurance to competitive bidding, they saved $404.8 million over five years -- money they were able to put into merit pay increases for teachers, and other classroom improvements.

Public union bosses want that money for themselves. They want to dictate spending decisions to state and local governments, and collect compulsory union dues to perpetuate their political power and line their coffers. The Supreme Court can end this unconstitutional coercion. The only way unions will be hurt by this is if the workers they claim to represent reject them.