As the state legislative session draws to a close, Gov. Cuomo and the state Democratic Committee are launching an online media campaign to push for an extension of his landmark property-tax cap.

It’s easy to understand why: Unlike many highly touted policy reforms, the tax cap’s actually working.

Which is why it should be made permanent.

Even adjusting for low post-recession inflation rates, property-tax increases since the cap took effect in 2012 have fallen significantly below long-term averages in every region of the state outside New York City (where the cap doesn’t apply).

The 2 percent cap on annual local property-tax levies, which Cuomo got through the Legislature five years ago, has had an especially dramatic impact on school taxes, which account for the lion’s share of New York’s exceptionally high property-tax bills.

In the 30 years before the limit took effect, school-tax levies grew at an average annual rate of 6 percent, nearly twice the average rate of inflation and even faster than the state’s total tax collections during that period.

But school taxes under the cap have risen by an average of just 2.2 percent a year, including allowances for voter-approved debt and new construction. Compared to previous trends, taxpayers have already saved billions.

In fact, not counting new taxes generated by property improvements, inflation-adjusted school-tax levies have decreased since 2012.

Because it holds down taxes across the board — for businesses, landlords and homeowners alike — the tax cap has a broader economic impact than targeted, state-funded rebates.

There’s just one problem: The tax-cap law is temporary, thanks to former Assembly Speaker Sheldon Silver, who rebuffed Cuomo’s effort to pass a permanent cap.

A convoluted provision says the cap will remain in effect as long as the state laws regulating city apartment rents are renewed beyond their expiration date, which next pops up in just two weeks.

Although important details aren’t settled, it seems likely the rent-control and rent-stabilization laws will be extended beyond their scheduled June 15 expiration. In that case, the tax cap automatically will be extended for at least the same length of time.
But the cap’s long-term survival isn’t assured. As long as it’s not permanent, the cap could be indirectly killed through manipulation of New York City rent laws.

Future governors will need Assembly and Senate cooperation to keep the cap in place a step ahead of the rent-law schedule — but, in a few years, both houses could be dominated by New York City Democrats uninterested in keeping the cap alive.

Wildly popular with the public, the tax cap is resented by public-employee unions — and loathed, especially, by the powerful New York State United Teachers, which has mounted a (so far) unsuccessful court battle to have the cap ruled unconstitutional.

County and municipal officials also want to drill more loopholes in the cap, claiming it isn’t flexible enough to allow for special needs and circumstances.

But the cap isn’t rigid: It can be overridden by a 60 percent vote of a locality’s governing body.

In the case of school districts, an override requires approval by at least 60 percent of the district residents voting in a budget referendum.

During the cap’s first three years, voters in 79 districts — 12 percent of the total — approved at least one override. This year, 11 out of 18 proposed school tax overrides were approved.

Cuomo has pledged to seek enactment of a permanent cap, and the Republican-controlled state Senate last month passed a bill erasing the tax cap’s sunset clause (with support from all the Democrats representing districts outside New York City).

But under Silver’s successor, Speaker Carl Heastie of The Bronx, Democrats remain the chief obstacle to making the cap permanent.

The end-of-session scramble will give the governor, backed by the Senate, optimal leverage to insist that the Silver sunset is removed.

To protect future taxpayers and to ensure his own legacy, Cuomo needs to remove any doubt that New York’s property-tax cap — with no added loopholes — is here to stay.