The U.S. Supreme Court may deliver a big blow to organized labor in America. On Monday, the court heard oral arguments in Friedrichs v. California Teachers Association, a case whose importance to public sector unions can hardly be overstated. If the oral argument was any indication, public sector unions are out of luck.

Friedrichs concerns the constitutionality of "agency shops" for workers providing government services. In an agency shop, people working under a collective bargaining agreement negotiated by a union are free not to join the union, but are required to pay the equivalent of the union dues. That's because without the rules of an agency shop, workers could get the benefits and protections of union membership without bearing any of the costs.

In 1977, the Supreme Court unanimously upheld agency shops in the public sector, subject to some restrictions. Unions could collect dues from non-members, but only for purposes related to employment and collective bargaining. Non-members could opt out of money used for political purposes.

The Republican Party, and hence a Supreme Court that has been largely controlled by Republican nominees since early in the Nixon administration, has moved far to the right since 1977. And the Roberts court has been chipping away at public sector unions. In the 2012 case Knox v. SEIU the court held that merely allowing non-members to opt out of political contributions violated their First Amendment rights. The court ruled that unions had to affirmatively get the consent of non-members to use dues for political purposes.

But that wasn't enough for opponents of labor. In 2014, in Harris v. Quinn, the court went further, arguing that agency shops violated the rights of home health care workers. In Friedrichs, the plaintiffs are essentially trying to make public right-to-work laws a constitutional requirement. The court is being asked to simply rule agency shops unconstitutional, full stop. This would starve unions of resources.

In theory, public sector unions should have had a reasonable chance of prevailing in the court. Justices Antonin Scalia and Anthony Kennedy have long held that the First Amendment rights of public sector employees should be minimal. In 1990 case, Scalia and Kennedy dissented from an opinion holding that it violated the First Amendment rights of public employees to be required to join the Republican Party as a condition of employment. If public sector employees can be compelled to join a political party as a condition of employment, it's essentially impossible to argue that they can't be required to pay dues for the benefits they receive from union representation.

But to be optimistic about Scalia and Kennedy assumes that they will put principle above politics. Alas, there's little reason to believe this. Most famously, Scalia and Kennedy's argument that the Affordable Care Act was unconstitutional was plainly inconsistent with Scalia and Kennedy's prior holding that the federal government could seize homegrown medical marijuana not intended for distribution. Indeed, the inconsistencies were so flagrant that Justice Ruth Bader Ginsburg's opinion holding the ACA constitutional in its entirety cited Scalia's earlier opinion chapter and verse.

Monday's oral arguments seem to make it clear that Scalia and Kennedy will decide the case based on the interests of the Republican Party rather than on their previous First Amendment doctrines. Both were relentlessly hostile not just to the arguments made on behalf of public sector unions, but to the unions themselves. Anybody holding out a hope that they may feel constrained by their previous opinions is surely disabused of the notion now.