The Port Authority of New York and New Jersey said this week that it is under investigation by the Securities and Exchange Commission, adding to the series of inquiries that have been ordered since the lane-closing scandal at the George Washington Bridge last year.

The disclosure came in a 228-page report on Thursday to potential buyers of the agency’s bonds, in which the Port Authority said the commission was conducting “a parallel investigation in one of the matters under review” by the Manhattan district attorney, Cyrus R. Vance Jr.

The inquiry by Mr. Vance’s office is focused, at least in part, on the agency’s handling of roadway construction projects, including the Pulaski Skyway and the Bayonne and Goethals Bridges, according to several people briefed on the matter who spoke on the condition of anonymity because that investigation is continuing.

About $1 billion in planned Port Authority spending was diverted to the Pulaski Skyway project, championed by the administration of Gov. Chris Christie of New Jersey. The bridge, connecting Newark and Jersey City, is operated by the state, not the Port Authority.