The Supreme Court’s ruling this week in Knox v. Service Employees International Union is one of the most brazen of the Roberts court. It shows how defiantly the five justices act in advancing the aggressive conservatism of their majority on the court.

The court’s moderate liberals were rightly dismayed by the majority’s willingness to breach court rules in pursuit of its agenda. In this labor union case, there is no getting around that the legal approach is indistinguishable from politics. The court’s five conservatives ruled that in 2005, Local 1000 of the Service Employees International Union should have sent a notice to all nonmembers it represented when it imposed a temporary 25 percent increase in union dues for public-sector employees in California to fight two anti-union ballot measures.

The court said the union infringed on the free speech rights of the nonmembers by not giving them the chance to prevent the use of their dues to support expressions of political views unrelated to collective bargaining. Justices Sonia Sotomayor and Ruth Bader Ginsburg agreed with this narrow judgment only.

This produced a 7-to-2 ruling on that specific question. But Justice Samuel Alito Jr., writing an opinion representing the conservative five only, went far beyond this principle, which has been settled law since 1986.