Prosecutors from the United States attorney’s office for the Southern District of New York and agents of the Federal Bureau of Investigation have found that the law firm, Goldberg & Iryami, P.C., has paid Mr. Silver the sums over roughly a decade, but that he did not list that income on his annual financial disclosure forms, as required, the people said.
The prosecutors, from the office of the United States attorney, Preet Bharara, and the F.B.I. agents were seeking to determine precisely what Mr. Silver, a Manhattan Democrat, has been doing for the payments, the people said. Spokesmen for the F.B.I. and Mr. Bharara’s office declined to comment.
Part-time work by legislators has long been a focus of federal investigators because corrupt lawmakers have used payments for ostensible part-time jobs or consulting work to mask political payoffs. It has also been a source of concern among government watchdog groups because of the potential for conflicts of interest.
The investigation into the Goldberg firm’s payments to Mr. Silver grew out of the work of the Moreland Commission, an anticorruption panel that Gov. Andrew M. Cuomo, a Democrat, created in 2013 but abruptly shut down in March. Before it was shut down, the commission had investigated how lawmakers earn money outside of Albany, though the inquiry was stymied by a legal challenge from lawmakers and their employers.
