Mayor Zohran Mamdani signed a controversial law Tuesday that gives nonprofits first dibs at buying distressed residential buildings in the Big Apple.

Hizzoner put his John Hancock on the Community Opportunity to Purchase Act — only the second bill he’s signed in the 11 months since he took office — after the City Council quietly resurrected a watered-down version of the bill last month.

The “COPA” law will affect about 2,100 properties across the five boroughs, officials said at Brooklyn news conference outside a Cypress Hills housing development.

“I am so proud today to sign COPA into law — a historic piece of legislation that will provide vetted community organizations with the right of first opportunity to make an offer on eligible buildings before they go to the open market,” Mamdani told reporters.

The bill was likely to become law even without the mayor’s back after it passed the City Council with a veto-proof 38-9 majority last month with the support of progressives and Council Speaker Julie Menin.

But the mayor actually signing the bill is a rarity in his tenure.

Critics have noted Mamdani has allowed more than 100 other bills to pass “returned unsigned” – a process that allows legislation to become law after four weeks if it sits on Hizzoner’s desk without a veto.

The law has come up multiple times but was called an “attack on private real estate ownership” before it was tweaked in recent weeks, eventually getting buy-in from some real estate groups.

City Council member Sandy Nurse (D-Brooklyn) said the compromise law will still be “the largest opportunity to purchase program in the country.

“Six years, six years, four introductions, four hearings, three mayors, two times it was passed, one time it was vetoed—that is the very short history of the Community Opportunity to Purchase Act,” Nurse said.

The law, which will go into effect one year from Tuesday, prevents landlords of primarily rent-stabilized buildings with outstanding housing code violations from listing their properties on the open market until they alert the city’s Department of Housing Preservation and Development.

Landlords then have to wait out a 20-day bidding window for qualified nonprofits to express interest in the property — and a maximum of 70 days to make an official first offer.

Owners aren’t required to accept the nonprofit offer and instead they may trigger a right of first refusal — which will allow them to negotiate a contract with an outside buyer. But the owners then have to go back to qualified nonprofits and give them the chance to match the third-party offer.

Under COPA, the nonprofit then has 15 days to match the outside buyer’s terms. If they do so, the landlord will be required to sell to the nonprofit over the outside buyer.

COPA does not apply to small landlords who own buildings with five or fewer units.