David Samson, chairman of the Port Authority of New York and New Jersey, listens at a board meeting on Feb. 19, 2014, in New York City. (Andrew Burton/Getty Images)

Federal prosecutors in Manhattan have subpoenaed the Port Authority of New York and New Jersey for records regarding the business dealings of the agency’s chairman, David Samson, according to media reports Monday.

U.S. Attorney Preet Bharara is interested, in particular, in potential conflicts of interest between Samson’s role as chairman and his private law firm, Wolff & Samson, the Wall Street Journal reported, citing anonymous sources.

Pressure has been building on Samson, an appointee of New Jersey Gov. Chris Christie (R), since his name surfaced in documents related to September lane closures at the George Washington Bridge, which connects New Jersey to New York City. Those closures caused gridlock over four days, allegedly as an act of political retribution against the mayor of Fort Lee, N.J.

Federal prosecutors and state lawmakers in New Jersey are conducting separate investigations into the lane closures. The probes have thrust Christie, his leadership style and his allies at the Port Authority into the spotlight.

The New York Times also reported the new probe Monday but said it was unclear why federal prosecutors in New York issued subpoenas when the lane closures are being investigated in New Jersey.

A spokesman for the Port Authority had no immediate comment.

When asked for comment, a spokeswoman for Samson referred to a statement from his attorney, Michael Chertoff, who said: “We are not commenting on the progress of investigations.”

“There continues to be a good deal of erroneous coverage of matters pertinent to my client,” he added. “That will become evident in due course.”

Critics have called on Samson to resign. Port Authority Executive Director Patrick Foye, who runs the day-to-day operations at the huge bi-state agency, said last month that Samson lacked the moral authority to remain in his post.

The next day, Christie defended his appointee, saying that he backed Samson “strongly and firmly.”