Federal prosecutors in New Jersey issued a subpoena last week to the Port Authority of New York and New Jersey seeking records relating to its chairman, David Samson, and contracts on two bridge projects worth $2.8 billion that he voted to award to construction companies with some ties to his law firm, according to people briefed on the matter.

The subpoena focused on Mr. Samson’s potential conflicts of interest. It was issued by the United States attorney’s office in New Jersey, which along with the Federal Bureau of Investigation is conducting a criminal inquiry into the lane closings at the George Washington Bridge and other suspected wrongdoing by current and former aides, appointees and associates of Gov. Chris Christie, the people said. They spoke on the condition of anonymity because the investigation is continuing.

The interest in Mr. Samson, a close political ally of Mr. Christie, represents a significant widening of the scandal that has grown out of the closing of two bridge access lanes in Fort Lee, N.J., in September. Emails between aides to Mr. Christie, a Republican, suggest the closings were politically motivated retribution against the Fort Lee mayor, Mark Sokolich, a Democrat, who had declined the Christie campaign’s entreaties to endorse him for re-election.

The grand jury subpoena came just days after the United States attorney’s office in Manhattan issued a similar subpoena to the Port Authority on Friday, March 7, and then, in an unusual move, withdrew it the following Monday.