Count New York’s government-employee unions among the biggest winners of this year’s budget battle — with taxpayers as the big losers.

In the dead of night, the Legislature adopted language that aims to protect public unions’ political power from a likely US Supreme Court ruling.

That ruling, expected this spring, would bar the mandatory collection of dues-like “agency fees” from non-members by declaring all public unions’ activities political, since they negotiate contracts with government, not private employers.

And forcing people to pay dues for political activity violates the First Amendment, the court is expected to rule.

Agency fees make up a key source of cash for public unions, as much as $110 million a year in New York, notes the Empire Center.

But in a pre-emptive strike, the Legislature (Republicans included) moved to let unions deny non-members covered by collective bargaining contracts all services (like free legal help) beyond salary and basic benefits — providing a powerful incentive for workers to join the union.

The bill also makes it harder for workers to withdraw, requiring the government to begin deducting dues within 30 days of someone being hired.

As Doug Kellogg of the watchdog group Reclaim New York told The Post: “It’s strong-arming government workers . . . to protect politically powerful special interests.”

Gov. Andrew Cuomo eagerly went along, claiming the high court is preparing to “effectively end public labor unions” — which (sadly) is nonsense on stilts. But such a ruling could threaten the unions’ revenue stream — and their destructive political clout.

That would be a real economic boost to all New Yorkers. Yet the Legislature did its best to protect the powerful.