This week’s US Supreme Court ruling in Janus v. AFSCME was not unexpected — and neither was the agitated, high-volume reaction from Gov. Cuomo and the public-sector union bosses who are his strongest political allies.

United Federation of Teachers head Michael Mulgrew sneered that backers of the Janus decision will need his prayers when they’re “all burning in hell.”

Tony Utano of the Transport Workers Union compared the judges to “Pinkertons in black robes” — alluding to the private detectives who helped violently break strikes in the early, 19th-century days of the industrial labor movement.

Danny Donohue, head of the state Civil Service Employees Association, said Janus “seeks to take away the freedom of working people to speak up for themselves, their families and their communities.”

And Cuomo issued an executive order based on the premise that the Janus decision “attempts to undermine worker safety and privacy.”

It was all a calculated distraction from the reality of the Supreme Court’s ruling — which puts the First Amendment constitutional rights of workers above the economic interests of government unions.

A 5-4 majority of the justices held that state and local government employees can no longer be forced to pay dues-like agency fees to unions they choose not to join — because, after all, everything a government union does, including collective bargaining, amounts to political activity designed to influence public policy.

The ruling means that about 1,700 different governmental entities in New York state — including New York City and the state government itself, as well as public authorities — must immediately stop taking money from nonmember employees. As of last year, the Empire Center estimated in a report on the Janus stakes, there were roughly 200,000 nonunion government workers paying $112 million in dues-like fees.

But the end of agency fees is just the beginning.

Another 1 million government workers in New York have joined unions assuming they’d have to pay one way or the other. Now they’ll have a choice. And experience elsewhere suggests many will choose to opt out.

In Michigan, about one in five teachers left unions when agency fees were abolished in that state beginning in 2013. Officials of AFSCME, the national parent union of New York City’s District Council 37, have estimated that 15 percent of their members would leave the rolls immediately if not forced to pay, and fully half would consider doing the same.

Here in New York, Cuomo has shown he’ll do his best to thwart workers attempting to exercise that choice. Cuomo’s new state budget includes statutory language designed to make it easier for unions to recruit newly hired employees and to trap workers into continuing to pay dues, or, as the governor characterized it, “protect union membership.”

To take advantage of a provision they essentially drafted, many New York government unions have changed their membership terms to make it next to impossible for employees to quit.

But it’s not clear they can get away with it. In his majority opinion, Justice Samuel Alito didn’t mince words: Involuntary payments to government unions are unconstitutional.

“Neither an agency fee nor any other form of payment to a public-sector union may be deducted from an employee, nor may any other attempt be made to collect such a payment, unless the employee affirmatively consents to pay,” Alito wrote.

In mounting a desperate rearguard action to protect the flow of cash from public-employee paychecks to union treasuries, Cuomo has been currying favor with the Democratic Party’s most powerful interest groups ahead of his September primary showdown with opponent Cynthia Nixon.

The late New York municipal labor boss Victor Gotbaum once put it, “We have the ability, in a sense, to elect our own boss.”

In other words, as usual, all of the interactions between government unions and elected officials ultimately boil down to political activity, which in turn implicates the First Amendment rights of any government employee forced to pay dues or fees to a union. So, in the end, Cuomo is proving the Supreme Court’s point.