The federal Government Accountability Office says it has begun probing toll increases on bridges in New Jersey, New York and Pennsylvania.
GAO spokesman Ned Griffith says the agency is looking into whether bistate transportation authorities are accountable.
The authorities, including the Port Authority of New York and New Jersey, were created by compacts approved by Congress.
The Delaware River Port Authority and the Delaware River Joint Toll Bridge Commission have both received requests for information from the GAO.
Both agencies operate bridges that connect Pennsylvania and New Jersey.
DRPA CEO John Matheussen told a board meeting Wednesday that he can explain why his agencies raised tolls from $3 to $5 between 2008 and last year.
US Sen. Frank Lautenberg, a Democrat from New Jersey, called for the investigation.