Twenty state workers in Maine are challenging the expenditure by the labor union that bargains on their behalf.
The nonmembers are required to pay a service fee for the union's collective bargaining efforts and contract administration.
The Service Employees International Union relies on portions of the fees to subsidize lawsuits concerning SEIU units other than Local 1989 to which the 20 current and former state employees belong.
At issue is whether a state can condition public employment on the paying of fees for such purposes.
This case is the latest instance of the justices addressing issues that could erode the power of labor unions. Last June, the court ruled that states may force public sector labor unions to get consent from workers before using their fees for political activities.
Three months ago, the court agreed to decide the validity of a state law that limits employers' ability to weigh in on union organizing.
Union officials have no legal authority to make nonunion public servants in Maine pay for union activity across the nation, said Stefan Gleason, vice president of the National Right to Work Foundation.