The state teachers union may wind up regretting coming out big for parental choice in the recent “opt-out” wars — because the same principle dictates support this month for Gov. Cuomo’s education-tax-credit bill.

This year, more than 200,000 Empire State students refused to take the state’s Common Core assessment exam, up from about 60,000 last year. In several districts, more than half the students opted out.

Perhaps the loudest voice pushing the “opt-out” message has been New York’s largest teachers union. Declaring its support for “a parent’s right to choose,” the New York State United Teachers have actively encouraged parents to opt their children out of the state tests.

NYSUT’s Web site even includes links to resources to help parents opt out if they “decide it is not in their children’s best interests.”

If test results are compromised by low participation, then the test-based accountability systems are toothless, and the union knows it. “Statistically, if you take out enough [students],” NYSUT president Karen Magee recently told reporters, “[the test] has no merit or value whatsoever.”

Parents, too, have legitimate concerns — about over-testing, a narrowing curriculum and the loss of local control over their children’s education. Frustrated at their diminished influence in the era of Common Core, parents are exercising one of the few tools they have left.

Of course, if the union really believed its own opt-out rhetoric, they’d realize that parents should be able to opt out of their assigned district schools as well. Cuomo’s proposed Parental Choice in Education Act would do just that.

Cuomo’s proposal would increase funding for public schools while also granting tax credits worth 75 percent of contributions to nonprofit scholarship organizations. These donations would help primarily low- and middle-income families enroll their children in private schools or in out-of-district public schools.

The proposal would also grant tax credits worth up to $500 directly to families earning up to $60,000 a year to cover tuition and fees at their school of choice.

For low-income students, school choice can be a pathway out of poverty. Unfortunately, although NYSUT has adopted the rhetoric of the school-choice movement, the union still vehemently opposes parents’ choice in where to send their kids to school.

Perhaps finding it impolitic to fight against low-income, minority children, NYSUT is engaging in magician-like misdirection. Magee and her allies are trying to recast the scholarship program as a “giveaway to the rich.”

One particularly juvenile and misleading NYSUT ad features a self-proclaimed “zillionaire” named “Mr. Moneybags” bragging that the law is designed to benefit the wealthy and their “exclusive schools.”

Rarely has such populist rhetoric been employed to oppose the interests of the poor — which is exactly what the union’s doing.

NYSUT’s chutzpah is all the more galling because donors do not financially benefit. That’s because although the 75 percent tax credits would reduce a donor’s tax burden more than a tax deduction, a donor concerned only with her bottom line would be better off not donating at all.

A $1,000 contribution would reduce a donor’s state tax liability by $750, but she would have given away a total of $1,250 in contributions and taxes rather than merely paying $1,000 in state taxes.

Nevertheless, it’s encouraging that even NYSUT finds it necessary to appeal to the choices of parents. The school-choice movement has won the battle of ideas in this regard.

In a recent poll by Harvard University and Education Next, 60 percent of respondents expressed support for education tax credits while barely a quarter were opposed.

By adopting the language of parental choice, NYSUT has had some success pushing back against the state test.

In doing so, ironically, the union has shown just how effective parents might be in chipping away at the laws that keep their kids trapped in failing schools — and the union power that depends on them.