In March, Mr. Carr issued a report claiming that Kushner Companies had falsified more than 80 work permit applications for 34 buildings. In July, 20 current and former tenants working with H.R.I. filed a lawsuit against the Kushners saying that they were forced out of their apartments at 184 Kent Avenue in Brooklyn by construction work that filled the building with “loud and obnoxious drilling” and a “constant cloud of toxic smoke and dust.”
“This is the beauty of our model, which is low cost, high impact,” Mr. Carr said as he fiddled with his ubiquitous laptop. “It’s all about publicly available data and connecting tenants to no-out-of-pocket legal support.”
Lucas A. Ferrara of Newman Ferrara, the law firm representing the tenants in the Kushner suit said, “Aaron has probably done more for rent-regulated tenants in New York City over the past three years than the city and state agencies have done in the last 20 years.”
But Adam Leitman Bailey, a lawyer representing or advising landlords in a number of the lawsuits, has a different perspective. “Aaron Carr is a very dangerous young man with his tongue,” he said. “I’ve never seen someone, aside from Donald Trump, who can manipulate the press as well as he does. At the same time, he is hurting and damaging the reputations of many innocent and reputable landlords.”
Mr. Bailey, who is well known for vigorously defending his clients in both the courts and the media, contends that many of the H.R.I.-inspired lawsuits are “frivolous.”
The State Supreme Court tossed out on technical grounds an H.R.I.-born class-action lawsuit against a company called Big City Properties claiming that the Harlem landlord had violated rent regulations at 11 buildings and inflated rents by overstating the cost of apartment improvements.
But the state’s Appellate Division recently reinstated many of the claims against Big City. Worried that the decision would make it easier for tenants to sue landlords, the industry’s powerful lobbyist, the Rent Stabilization Association, has asked permission to join a possible appeal by Big City to the state’s highest court.
In 2014, he ran Michael Blake’s successful campaign for an Assembly seat in the South Bronx and subsequently became Mr. Blake’s chief of staff. In that role, Mr. Carr said he would repeatedly call city and state agencies on behalf of tenants tangling with landlords, pleading for inspectors to visit their buildings.
“It was like waiting for Superman,” Mr. Carr said, “but Superman never came.”
Mr. Carr formed H.R.I. in 2016 with “a couple thousand dollars” of his own money, and has relied on a “bottom-up enforcement approach” of scrutinizing records at the city’s Finance and Building departments and the state’s Division of Housing and Community Renewal, which oversees the city’s one million rent-regulated apartments.
Today, H.R.I. has two full-time and one part-time employees, including Mr. Carr, and a budget of $225,000, much of which comes from individual donations and the Robin Hood Foundation, a charity dedicated to fighting poverty.
Robin Hood’s board includes Jeff T. Blau, chief executive of Related Companies, one of the city’s biggest developers; and Paul Tudor Jones II, a hedge fund manager.
The bulk of the lawsuits filed have been related to violations of the city’s J-51 housing program, which grants tax breaks to landlords of rental apartments who invest in new roofs, boilers and elevators. Building owners are prohibited from deregulating apartments as long as they receive the tax benefits.
In one H.R.I.-initiated lawsuit, against Argo Real Estate, a building owner and property manager, lawyers contend that Argo improperly deregulated 369 rent-regulated apartments at nine buildings in Queens, while getting more than $1 million in tax breaks.
A lawyer for Argo, which has not responded to the complaint, declined to comment. One of the lawyers who brought the suit, Shaina Weissman, said that the two sides have been in settlement discussions, but that little progress had been made.
Mr. Carr and H.R.I. have not left the state, which oversees rent-regulated housing, off the hook.
In May, Mr. Carr sued the state for refusing to release the names of “cheating landlords” who have been caught defrauding the J-51 program in audits that Gov. Andrew M. Cuomo’s administration began in 2016. The suit sought to compel the Division of Housing and Community Renewal to release the names.
Mr. Carr complained that legislators do not have the will to enforce the laws already on the books, because a steady flow of political contributions at a state level come from the real estate industry.
“New York State’s broken campaign finance laws have turned housing enforcement into a real estate protection system,” he said.
H.R.I. also says city agencies have failed to aggressively go after unscrupulous landlords. This month, Mr. Carr released a report saying that the city has failed to collect $1.5 billion in fines from landlords for violations ranging from “loose rubbish” to failure to notify authorities of asbestos, including more than $350,000 it said was owed by the Kushner Companies.
Aziza Taylor, a spokeswoman for the city’s Department of Finance, said that H.R.I. has “surfaced a legitimate issue regarding the difficulty in collecting” fines from landlords. Officials acknowledge that there often are disconnects in the system designed to protect tenants, with city and state agencies using different data systems, and poor communication between the city agencies that issue violations and the Finance Department, which is supposed to collect the fines.
A building’s owner is often a limited liability company and a landlord may hold numerous buildings, each in a separate L.L.C.; the finance department often does not know the name of the company or individual behind them.
Ms. Taylor said the agency is proud of the work it has done in recent years to get landlords to pay their fines.
According to the Finance Department, the Kushners owe $197,000 in unpaid fines, but have paid $108,000 in penalties issued for the past eight years.
But that figure does not include $210,000 in fines assessed by the Buildings Department in August. The city’s action came after the March H.R.I. report saying that the company had filed dozens of construction permits falsely claiming that no rent-stabilized tenants lived in 34 of its buildings.
The Kushners, who have described many of the building violations Mr. Carr has unearthed as “paperwork errors,” or problems created by tenants themselves, declined to comment.
Mr. Carr said he is not obsessed with the Kushners, but they are a convenient foil to get media attention for government’s lax enforcement of laws protecting tenants.
“Sometimes a sleepy government needs a very big wake-up call,” he added. “It is notable that while our state and city government have been out ‘resisting’ the White House, it has allowed landlords like Kushner to invade its own house. Our existence is a window into a broken enforcement system and a broken democratic system.”