The US Supreme Court will hear oral arguments Monday in Janus v. AFSCME, a landmark case that could end the mandatory payments public employees make to unions.

For union-dominated New York, this is a very big deal.

The background: Mark Janus, an Illinois state government worker, argues the payments he’s forced to make to the American Federation of State, County and Municipal Employees constitute compelled political speech, since the union uses the money to influence government. This, he says, is the same as forcing him to pay a lobbyist, and therefore violates his First Amendment rights.

Two years ago, a California teacher was on the verge of prevailing in a similar case that ended in a tie vote after the untimely death of Justice Antonin Scalia. With Justice Neil Gorsuch in Scalia’s seat, court watchers expect a victory for Janus.

If that happens, close to 200,000 New Yorkers who haven’t signed union-membership forms can immediately stop having these “agency fees” withheld from their pay, saving them a combined $110 million a year.

Government unions have been scrambling for years to convert these fee-payers into members who consent to the deductions. Thanks to New York’s agency-fee law, employees must pay the union one way or the other, so signing up didn’t affect their paychecks.

If the high court ends compulsory agency-fee collection, many of the roughly 1 million New Yorkers who are now members of a government union are likely to quickly reconsider.

If the union doesn’t trap them first.

New York’s government unions have been urging workers to sign new union-membership forms designed to lock them into paying annual dues that typically range from about $600 for unskilled, lower-paid workers to more than $1,000 for some teachers and other professionals.

For example, New York State United Teachers has begun encouraging members to sign a new membership document (also commonly known as a union “card”) that would allow them to opt out only during the month of August — which happens to be among the busiest parts of the year for teachers. The document requires teachers and others covered by NYSUT contracts to promise to keep paying dues “regardless of whether I am or remain a member of the union.”

The Professional Staff Congress, a NYSUT local representing more than 27,000 CUNY faculty and staff, recently released a “new, stronger union membership card.” The form, which existing members are also being pushed to sign, is “stronger” because it limits workers to just a 10-day opt-out period each year. To further confuse everyone, the period would vary for each worker depending on when he or she signs.

For now, such agreements are unenforceable. That’s because they’re superseded by Section 93B of New York’s General Municipal Law, which gives government workers the right to opt out of union membership at any time, merely by asking their employers.

But government unions are lobbying hard for a bill that would eliminate workers’ 93B protections. A legislative sponsors’ memo misleadingly describes the bill as an innocuous effort to “streamline” collective bargaining in New York. But one big state union, the Public Employees Federation, let the cat out of the bag in a recent newsletter item, openly touting its push to “make it more difficult for state employees to quit unions and stop paying dues.”

The anti-workers’ rights bill passed the Assembly last year and recently cleared a Senate committee without a single vote in opposition. Unions apparently are confident they can ram it through to Gov. Cuomo’s desk. In his State of the State Address, Cuomo loudly pledged to stand with them.

The stakes are enormous. Between 2013 and 2016, which included one statewide election and two legislative election cycles, New York’s government unions collectively spent $43 million on lobbying — more than New York’s largest real-estate, hospital, tobacco and trial-lawyer interests combined. During the same period, unions spent $52 million out of their political-action committees.

A ruling for Janus would be a win for workers, forcing unions to focus more on treating their members like paying customers — and less on squeezing taxpayers.

Ken Girardin is an analyst at the Empire Center for Public Policy.