More New Yorkers are joining the legal battle against the state’s new pied-á-terre tax — with one claiming the city mailed his notice letter to a neighbor who lives nearly 30 stories below him, court documents show.

Four new plaintiffs have jumped onto the lawsuit filed by attorney Randy Mastro that seeks to pause the surcharge on luxury second homes in the Big Apple due to the Mamdani administration’s botched rollout of the new tax.

Among them is Kenneth Fishel, a real estate executive, who claims he was targeted with a letter from the city Department of Finance alerting him that he could be subject to the levy — despite paying taxes for years out of his Park Avenue co-op on the Upper East Side, the Tuesday filing shows.

But the DOF allegedly mistakenly labeled the letter, mailing it to one of Fishel’s neighbors who lives nearly 30 floors below him.

“Fishel only learned of and obtained a copy of the notice because he ran into his neighbor living 27 floors below him on the elevator,” the suit states.

The 17,000 notices sent out by the DOF alert property owners that they could be subject to a five-figure tax bill — unless they file for an exemption — under the law approved by state lawmakers and Gov. Kathy Hochul in the spring.

All of the new plaintiffs on the suit — who claim primary homes in Chelsea and the Upper East Side — say they filed for exemptions to the tax, but haven’t been granted them yet, the filing shows.

They claim they faced  issues navigating the city’s “tangled morass of an exemption regime,” despite not being subject to the surcharge, which covers one- to three -family homes worth at least $5 million and co-ops and condos valued at $1 million or more that are unoccupied, non-primary residences.

The plaintiffs will “continue to suffer irreparable harm in attempting to apply for an ‘exemption’ to a tax that was not designed to burden them in any way,” they claim in the suit.

A Staten Island judge granted a temporary pause to the tax rollout after the suit was initially filed earlier this month, but that ruling was overturned by an appellate court after Mayor Zohran Mamdani’s administration pushed back.

Mastro, in a letter to that same Staten Island judge, argued the new plaintiffs would “eliminate” the “specious mootness arguments” made by the city that one of the original New Yorkers who sued was granted an exemption to the tax after filing for one.