MTA chairman Joe Lhota is under fire from the watchdog group Common Cause New York, which is calling on the state to investigate potential conflicts of interest.

Lhota, who is also senior vice president, vice dean and chief of staff at NYU Langone Medical Center, is breaking the law by serving as chairman of the agency while also being registered to lobby on behalf of NYU, charged Susan Lerner, the executive director of Common Cause’s statewide chapter.

Lerner wrote a letter, dated Nov. 15, to the state’s Authorities Budget Office, requesting an investigation into the matter.

“It’s an apparent conflict of interest for the head of the MTA to actively lobby for another organization. Mr. Lhota is not exempt from the rules — he should discontinue lobbying immediately,” Lerner said in a statement. “The ABO should investigate Mr. Lhota swiftly and act accordingly.”

During a news conference after an MTA board meeting Wednesday, Lhota dismissed any notion he is breaking the law, pointing to his unique appointment. Unlike his predecessor, Tom Prendergast, who was salaried as jointly MTA chairman and CEO, Lhota is working per diem as chairman, with CEO duties delegated out.

Lhota said he had reached out to the state’s Joint Commission on Public Ethics (JCOPE) to make sure he had proper legal footing after Gov. Andrew Cuomo tapped him for the position at the transit agency in June.

“Thinking that this would possibly ever become an issue, when I accepted this position [I] had discussions with and communications and writing back and forth with JCOPE, where it’s been determined that I am not an employee of the MTA. I’m a per-diem; I’m like any other board member,” Lhota told reporters. “I have a right to do work somewhere else — in this case NYU Langone Medical Center. I have not lobbied in this job, though I’m not prohibited from it.”

An email addressed to Lhota from Seth Agata, the executive director at JCOPE, appears to back up Lhota’s explanation.

Under the structuring of the chairman position, “you would not be considered a ‘state officer or employee’ for purposes of Public Officers Law Section 73 and not be subject to its strictures,” Agata wrote in a letter dated Sept. 28, 2017, which was provided by the MTA.

Lhota appeared exasperated Wednesday after sitting through a rather grim MTA forecast that outlined the need for new revenue sources to bridge an increasing budget gap, as well as more fare and toll hikes in 2019. As he called the meeting into executive session, Lhota stared at his cellphone and was caught on a hot mic saying, “Like I don’t have enough [expletive] problems.”