Jakub Markowski made more money than the mayor of New York City last year. He made more than the police commissioner, the fire commissioner, and the people running the city’s schools and jails. In fact, he made more money than nearly every member of New York’s roughly 350,000-person municipal work force.

He works as a plumber supervisor for the city’s public housing agency and was paid for almost 2,560 hours of overtime in the 2025 fiscal year — more than any other city employee — bringing his annual earnings to $465,000. What’s more, permits filed with the city show that Mr. Markowski was running two private plumbing businesses at the same time.

That extraordinary workload is now under scrutiny.

The city’s Department of Buildings is investigating Mr. Markowski’s work practices, a spokesman confirmed, including whether the arrangement violated rules designed to ensure that plumbing work, which can involve dangerous gas pipes, is done safely.

The questions about his conduct come as the housing agency, the New York City Housing Authority, faces enormous financial and infrastructural woes. Almost 300,000 people live in more than 240 public housing developments across the city, according to agency data. Many of those buildings are in poor condition. The system needs tens of billions of dollars in repairs and upgrades, according to the latest city estimate.

The constant care required to keep buildings running is one reason Mr. Markowski, a licensed master plumber, and other skilled workers at the agency regularly end up working huge amounts of overtime. And it is not uncommon for licensed master plumbers in New York to earn salaries over six figures. But the sheer volume of hours and pay that Mr. Markowski accrued that year at his city job — an average of about seven extra hours per day if he worked for 365 days straight — is unusual.

Mr. Markowski did not respond to several requests for comment. Reached by phone on Monday evening, he said he was busy working and hung up.

Buildings Department records show that between July 1, 2024, and June 30, 2025, the same period Mr. Markowski logged his overtime, his businesses — Super Plumbers Corp. NYC and Dynamic Blue Water Mechanical — worked on more than 70 projects in affluent neighborhoods like Brooklyn Heights and Manhattan’s Upper East Side.

In 2019, Mr. Markowski obtained a waiver from the city allowing him to do both public and private work, according to Barbara Brancaccio, a spokeswoman for the housing authority. The city grants a few hundred such waivers every year. The year after receiving the waiver, Mr. Markowski was paid for more than 1,840 hours of overtime.

In 2024, though, Mr. Markowski was promoted to a supervisory position on a fire safety team. While he was required to request a similar waiver in that role, he did not do so, Ms. Brancaccio said.

The Plumbing Foundation City of New York, a nonprofit trade group, filed a complaint with the Buildings Department last year, raising concerns about Mr. Markowski’s “questionable work arrangements,” according to a June 2025 email sent to the department.

“Enabling one individual to run a private plumbing business while serving as a city plumbing supervisor and accruing more overtime than any other city employee is beyond wasteful, and it raises serious concerns about the integrity, safety and oversight of NYCHA’s building operations,” April McIver, the group’s executive director, said in a statement.

Ms. Brancaccio of the housing authority said that the Plumbing Foundation did not represent the agency’s interests and that all public employees must follow conflicts of interest law.

Overtime abuse and other ethical issues have roiled the housing authority. In 2024, federal prosecutors brought bribery and extortion charges against dozens of its employees. Two years before that, the agency fired at least 18 people after an investigation into overtime fraud.

In addition to his fire safety job, Mr. Markowski has a “secondary role” as a backup plumber supervisor, handling emergency responses on nights and weekends, according to Ms. Brancaccio. Asked for an accounting of the work Mr. Markowski did to earn his overtime pay, the authority said it would provide that information in response to a New York Times request made under state freedom of information laws. That request has not yet been fulfilled.

Asked whether NYCHA was investigating Mr. Markowski’s work arrangement or overtime, the agency referred questions to the city’s Department of Investigation.

“This is an ongoing matter at D.O.I., and we decline further comment,” said Diane Struzzi, a spokeswoman for that department.

The city has also investigated safety scandals in the plumbing industry, including a fatal gas explosion at an East Village building in 2015 that killed two people and injured more than a dozen. The authorities in that case criminally charged a licensed master plumber who had let an unlicensed plumber use his license to perform gas-line work; the unlicensed plumber was convicted of manslaughter.

Mr. Markowski’s two businesses share an address in Maspeth, in central Queens. During a recent visit, a small sign in the building’s window displayed Mr. Markowski’s name and the name of Super Plumbers.

Inside, “Dynamic Blue Water Mechanical” was splashed across one wall in bright blue letters. A woman taking phone calls at a front desk said Mr. Markowski was not there. Asked about his whereabouts, the woman, who said she worked for Mr. Markowski, said she would have to call her “other boss,” a man named Robert Tarnawa.

Mr. Tarnawa, who filed a certificate of incorporation with the state for Dynamic Blue in 2022, did not respond to several requests for comment.

The relationship between Mr. Markowski and Mr. Tarnawa, who is not a licensed master plumber, is unclear. Three general contractors who worked on projects that list Mr. Markowski as master plumber said in interviews that they had vague, if any, memories of Mr. Markowski, but that they did remember Mr. Tarnawa.

The Buildings Department said that Mr. Markowski’s relationship with Mr. Tarnawa was one focus of its investigation.

City law says that plumbing work must be done either by a licensed master plumber or by someone working under that person’s “direct and continuing supervision.” It is not clear whether any other master plumber was involved with the work done by Mr. Markowski’s companies.

Andrew Rudansky, a spokesman for the Buildings Department, said whether a specific business arrangement violates the law “depends on the specific circumstances of the case, which would be determined through an investigation.”