The Supreme Court is listening to oral arguments today in Janus v. AFSCME, a case that could significantly impact public sector labor unions and the public sector employees who pay dues to those labor unions.

At issue is whether public sector unions can require the payment of either union dues or “fair share fees” from those employees in bargaining units that those unions represent. A Supreme Court decision that prohibits unions and employers from agreeing in a collective bargaining agreement to require such payments will significantly cut into the revenue of public sector unions.

Today is not the first time the Supreme Court has reviewed the legality of requiring public sector employees to pay union dues. In 1977, the Supreme Court decided Abood v. Detroit Board of Education, a case that allowed unions to demand the payment of dues but required unions to offer employees the ability to pay what has come to be known as “fair share fees,” a payment that purports to not include amounts for certain political activities.

Much more recently, the Supreme Court heard oral arguments in Friedrichs v. the California Teachers Association, a case very similar to the Janus case. In fact, it was expected that the Supreme Court would have found such payments to violate the First Amendment Rights of public sector employees had Justice Antonin Scalia not passed away prior to the announcement of the decision. Because Justice Scalia could not join in the decision, the Supreme Court deadlocked 4-4 and the opinion of the lower court, which had allowed the payments, was upheld.

In the last year, Justice Scalia was replaced on the Supreme Court by Justice Neil Gorsuch, who, like Justice Scalia, is seen as a key piece of the conservative majority on the Supreme Court. Most who have followed this case and the workings of the Supreme Court believe that Justice Gorsuch will follow his conservative colleagues and make mandatory payments to unions by public sector employees unlawful.

While the decision is not expected for some time, labor unions are already planning for this likely outcome. Figures that have leaked out from some of the leading unions that represent public sector employees suggest possible membership declines of 20 to 30 percent. Because unions have no significant ways to make money other than by dues, such a membership decrease will result in a revenue decrease in the same range.

In some cases, unions are already attempting to get in front of the decision by contacting employers with which they have a labor agreement and “spinning” the likely outcome by informing the employers of the number of current “fair share” participants who will be impacted by the decision and by advising the employers that they should immediately stop the remittance of fair share payments upon notice by the specified employees or the union. Of course, unions are leaving unsaid the fact that many others may follow when they learn of the impact of the expected Janus ruling.

Instead of merely relying on these communications, public sector employers with unions must carefully monitor the court’s activity in the Janus case and prepare for the decision. A decision that makes unlawful the mandatory payment of dues or fair share fees may significantly affect the ability of some public sector unions to bargain effectively and provide substantial legal support in grievance and arbitration proceedings. Public sector entities should review the impact the ruling may have on their public sector unions and should determine how they are going to communicate these potential changes to unionized employees.

At the same time, public sector entities that are either completely or partially non-union should take time to evaluate whether they are vulnerable to union organizing and determine their position regarding union organizing. Not only will unions attempt to replace lost revenue with new members, but a key message many employers use to combat unionization during organizing drives, that unions may not be worth the cost of the dues that all employees must contribute, may also no longer apply if employees no longer have the legal requirement to pay union dues.