More trouble may be on the horizon for New Jersey Gov. Chris Christie, as the office of Manhattan District Attorney Cyrus Vance is now reportedly investigating the relationship between the Republican and the Port Authority of New York and New Jersey.

In January, reports surfaced that aides working for Christie conspired with the governor’s appointee at the Port Authority in September to close traffic lanes in Fort Lee, N.J., leading to the George Washington Bridge, seemingly for political retribution.

Christie said he was not aware of the lane closures or of the political motivations behind them. He has since fired the aides responsible, and his appointee at the Port Authority stepped down before the scandal broke. In March, Port Authority Chairman David Samson resigned as well. Five people close to Christie have either been fired or resigned amid the scandal. This scandal has been a major distraction for Christie as he contemplates a 2016 presidential run.

The latest subpoenas, first reported last week in the Wall Street Journal, add to a growing list of investigations into the Port Authority and bridge scandal. The summonses are probing into whether Christie’s administration and the Port Authority cooperated in the rebuilding of the World Trade Center site, the PATH transportation center in Manhattan and assorted projects in New Jersey.

Several people familiar with the matter told the Wall Street Journal that Port Authority Commissioner Anthony Sartor, who is responsible for managing the reconstruction of the World Trade Center, is expected to step down.

New Jersey state legislators and federal investigators, led by U.S. Attorney Paul Fishman, are conducting their own probes.