Current federal law allows unions to collect so-called "fair-share" fees from non-members who benefit from the agreements that unions negotiate on the non-members' behalf. But that could change, and deal a devastating blow to public-sector unions, if the U.S. Supreme Court rules the way many court-watchers expect it to.

It's difficult to separate the legal questions from the political ones raised by Friedrichs v. California Teachers Association, a case in which a group of public-school teachers who oppose positions taken by their union claim they should not be compelled to subsidize speech by a third party they don't wish to support. Oral arguments in the case were heard this week.

The legal question is a vexing one. It seems reasonable to assert that public employees - or anyone -- shouldn't be forced to contribute to an organization with which they fundamentally disagree. But it's also easy to understand that many who do agree would be tempted to withdraw their contributions if they knew they would still reap the benefits of union representation.

The practical impact of a court ruling overturning fair share fees would vary dramatically by state. Almost half the states currently have "right-to-work" laws that forbid compelling anyone to join a union or contribute fair-share fees. But the landscape is dramatically different in some other states.

In Massachusetts, for example, 18 of the 20 political action committees that contributed the most to candidates for state and county offices during the last election cycle for which data exists were labor organizations. And recent revelations about labor issues at the financially troubled Massachusetts Bay Transportation Authority (MBTA) highlight the price taxpayers pay when unions wield too much power.

Nearly one-quarter of MBTA employees earned six figures last year, and labor costs account for more than 70 percent of overall operating expenses. (One maintenance worker whose salary was $85,000 pulled down a total of $315,000 in 2015 thanks to overtime.) A collective-bargaining loophole allows workers who work less than 40 hours to collect overtime by being paid for sick time, then working an extra shift during the same week.

The MBTA's bus and subway operators are the best paid of any major U.S. transit agency and will be receiving among the largest raises over the next two years. One reason is that the MBTA has "final and binding arbitration," a highly unusual system under which arbitration rulings are not subject to approval by any elected or appointed body. The provision also creates a disincentive for unions to settle matters at the bargaining table.

As one who took more than six years to graduate at the bottom of my law-school class, I'll leave the legal questions raised by Friedrichs to the august justices of the Supreme Court. But from a policy perspective, the best result would be for the court to protect workers by upholding fair-share fees and for states in which taxpayers are harmed by excessive union political muscle to eliminate provisions that invite abuses like those enjoyed by MBTA workers.

The problem, of course, is that those states are the ones in which the political environment makes it the most difficult to pass legislation that curbs union abuses.

This column has been updated to correct the title of the lawsuit before the Supreme Court.