NEW YORK — New York’s largest transit union is making preparations to launch legal action against Mayor Eric Adams’ top aide, Randy Mastro, and several other politically connected individuals over their efforts to ban the city’s horse carriage industry.

A lawyer for the Transport Workers Union, which advocates for city horse carriage drivers and opposes a ban, disclosed its plans to sue in letters sent this week to Mastro and the others. The letters, copies of which were obtained by the Daily News, claim Mastro and the others were involved in a “deceptive enterprise,” though they don’t go into detail about the allegations. The letters demand the recipients preserve records related to their effort to outlaw the carriage industry.

The missives were sent after The News reported last week that Josh Fox, a Florida businessman, met privately with Adams and Mastro days before the mayor on Sept. 17 came out in favor of abolishing the industry, reversing his previous opposition to such a ban.

Fox, an Adams campaign donor, runs the Hunter Brady Foundation, an animal rights group that has sought to manufacture electric carriages that’ could replace Central Park’s horse-drawn buggies. A top executive at Fox’s foundation is Eric Lerner, another Adams donor who helped run the largest super PAC that supported the mayor’s reelection bid before he abandoned it last month.

In his letters, the TWU attorney, Matt Richard, wrote that the union believes Fox, Lerner, their foundation and NYCLASS, the animal rights group that has spearheaded efforts to ban the horse industry, may have engaged in “possible misrepresentation, improper fundraising, deception of donors and lobbying violations” as part of their anti-carriage push.

Citing an investigation by the union, Richard wrote in the letters that the TWU also suspects involvement by Mastro, NYCLASS executives Steve Nislick and Edita Birnrkrant, lobbyists Corey Johnson and Jason Goldman as well as two City Council members, Bob Holden and Erik Bottcher.

Holden and Bottcher have introduced a Council bill that would sunset the carriage industry, while Goldman has represented NYCLASS as a lobbyist. Johnson, an ex-Council speaker who used to employ Goldman as his chief of staff, has been lobbying for the Central Park Conservancy, which came out in favor of a horse carriage ban in August.

TWU International President John Samuelsen declined to elaborate further on his union’s findings, but said he “strongly believes” there’s an effort afoot to “monetize the cessation the Central Park horse carriages, through real estate development and the procurement of electric touring vehicles.”

Richard said all the individuals referenced in his letters as well as “other consultants and lobbyists” are expected to be named as defendants in the suit, which he added is likely to be filed “in New York and/or Florida.”

Frank Carone, Adams’ longtime political confidant, worked for Fox in 2023 to get his electric carriage plan in front of city officials. Carone wasn’t mentioned in Richard’s letters.

Spokespeople for Fox’s foundation didn’t immediately comment, and neither did Johnson, Goldman, Holden or Bottcher.

Mastro, who represented NYCLASS as a lawyer before becoming Adams’ first deputy mayor this year, referred to City Hall spokeswoman Kayla Mamelak, who called the TWU legal threat “frivolous and an obvious PR stunt by a campaign that’s getting more desperate every day.”

“More than 70% of New Yorkers agree that it’s time to end horse carriages for the safety of pedestrians, cyclists, drivers and animals alike,” Mamelak said, citing recent polling. “Let’s tune out this noise, follow Mayor Adams’ lead, and get it done as a matter of public safety and the humane treatment of these magnificent animals.”

Birnrkrant, NYCLASS’ executive director, said Richard’s letters are “clearly meant to intimidate and silence the truth.”

“For several weeks TWU leadership has been running a desperate intimidation campaign straight out of Donald Trump’s playbook — full of bullying, unhinged lies and misinformation,” said Birnkrant, whose group recently accused Samuelsen of defaming NYCLASS.

Animal rights advocates have pressed for years to abolish the carriage industry over concerns about the horses’ health. The TWU says an end to the industry would deprive its members of their livelihoods while arguing there are ways to ensure horse safety without a ban.

Before he became mayor, Adams said in 2021 he would oppose an outright ban.

But last month — less than two weeks before he dropped his reelection bid amid continued fallout from his corruption indictment — Adams announced he backs a ban and urged the Council to pass the Holden-Bottcher bill. In explaining his reversal, Adams said he was moved to act by a video of a carriage horse breaking loose and running panicked through Midtown.

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