The Mamdani administration responded to concerns about the bumpy rollout of its second-home tax, stating it had reduced the rolls of property owners who may owe the tax by over 4,000 and extended the deadline for homeowners to prove New York City residency. The city’s statements, offering its most detailed defense yet of the complicated process, came in a court filing in a lawsuit brought by property owners arguing the city mishandled the tax’s introduction. Last month, the Finance Department notified about 17,000 property owners they might be subject to the tax on high-end “pieds-à-terre” unless they could prove primary residence.

The tax applies to condos and co-ops valued at $1 million or more used as second homes, and one-, two-, and three-family homes valued over $5 million. It was sought by Mayor Zohran Mamdani to raise taxes on the wealthy. The lawsuit, filed on Staten Island, does not challenge the tax’s legality but argues the city sowed chaos by sending notices without first determining residency and releasing a list of nearly one million properties that included owners’ names.

Judge Wayne M. Ozzi paused the rollout, but the city appealed, staying the order. On Tuesday, the city said 2025 tax data established residency for about 1,200 of the 17,000 notified owners, approved proofs for another 2,900, and was still reviewing 2,600 more.

It is sending new notices to 10,800 owners based on 2025 data and extended the deadline to prove residence to Oct. 6 from Sept. 18. The city defended the notice process as intentional design of the law. Randy Mastro, lawyer for the property owners, called the filing “an admission that this was a massive screw-up,” saying the city should have used 2025 tax data initially and extended the deadline to Oct. 16.

The lawsuit continues as thousands remain in limbo. The city seeks dismissal, claiming plaintiffs showed no meaningful harm and that proving primary residence is straightforward.