While some union foes called the court's ruling an important victory and predicted that it would lead to other such laws, the National Right to Work Committee acknowledged that it decided a narrow issue.

The justices did not say it was unconstitutional to require teachers and other public employees to pay dues to a union. Rather, they said only that states that allow public sector unions may also protect the rights of dissidents.

At issue before the court was a unique Washington state law that said unions may not collect fees from a nonmember and spend this money on politics unless "affirmatively authorized by the individual."

The state's largest teachers union challenged this rule in court. The Washington Supreme Court struck down the restriction as a violation of the union's rights, but the ruling was overturned by the Supreme Court.

"Unions have no constitutional entitlement to the fees of nonmember employees," said Justice Antonin Scalia. "It is undeniably unusual for a government agency to give a private entity the power, in essence, to tax government employees," he wrote, referring to the "agency shop" laws in many states that permit such arrangements in the public sector.