Updated 8:05 p.m. ET, 2/10/2014
Trenton, New Jersey (CNN) - A joint state legislative committee investigating the traffic scandal in New Jersey that has roiled Gov. Chris Christie's administration plans to issue more than a dozen new subpoenas.
Sources familiar with the matter told CNN that 18 subpoenas will be issued on Tuesday. Four will go to individuals or offices that have been served once already.
Those to be issued subpoenas for the first time include the custodian of records for the State Police aviation unit and the custodian of records for the Port Authority of New York and New Jersey.
Several more employees in Christie's office are also on the list, the sources said.
So far, investigators have subpoenaed 20 individuals and groups, including top administration and political advisers to Christie.
The governor, himself, has not been served with a subpoena, but his office in general has.
State legislators and the U.S. attorney's office are investigating suggestions top Christie appointees orchestrated traffic jams over several days last September 9 through 13 by closing access lanes to the George Washington Bridge in Fort Lee to politically punish that town's mayor for not endorsing the governor for reelection.
Christie has denied knowing anything about the gridlock until after it occurred, and has said he knew nothing about any political mischief by members of his administration.
The scandal has called into question Christie's swagger and his blunt governing style, which has been a positive with voters through two gubernatorial elections, and has clouded his prospects as a potential 2016 presidential candidate.
In a new twist, legislative investigators want to know whether Christie flew over the traffic gridlock in a State Police helicopter while returning to Trenton from a 9/11 event.
This could be important because Christie has said he knew nothing about the traffic mess until it was over and surfaced in media reports.
Moreover, investigators want to know if David Wildstein, a top Christie appointee at the Port Authority at the time who is at the center of the bridge-lane closure scandal, was aboard.
A Christie spokesman told CNN that Christie used the copter to travel from New York to Trenton following the 9/11 event and said Wildstein "did not ride with the governor."
What's unclear, however, is whether Christie flew over the George Washington Bridge, which is well north of where the ceremony took place at "Ground Zero" in lower Manhattan.
There are also questions about how Christie's administration handled the distribution of Superstorm Sandy relief money to the city of Hoboken.
Mayor Dawn Zimmer has alleged that members of the governor's administration conditioned storm relief on her support for a redevelopment project backed by Christie.
Those officials, including Lt. Gov. Kim Guadagno, vigorously deny the allegations.
In a new development in that matter, Zimmer's office has declined to provide documents and take part in a private interview with Christie's office as his team of lawyers conducts its own investigation.
Randy Mastro, who represents Christie's office, wrote to multiple members of Zimmer's office on February 4, asking for their assistance.
But in a letter of their own two days later, Zimmer's lawyers questioned the appropriateness of the governor's office "investigating itself" when there is already a federal probe underway.
U.S. Attorney Paul Fishman is also looking into Zimmer's allegations as well.