TRENTON, N.J. — A New Jersey legislative panel intensified efforts Monday to force two key aides to Gov. Chris Christie to turn over documents related to traffic gridlock near the George Washington Bridge as it authorized 18 more subpoenas.

Recipients in the third round of subpoenas include executives at the Port Authority of New York and New Jersey, the agency that runs the bridge; a failed Supreme Court nominee who Christie later named to the bridge agency; and the state police aviation unit, which could provide information about Christie’s helicopter travel during the time the lanes were blocked for four days in September.

Christie’s office acknowledged Monday that the governor, who travels frequently by helicopter, flew to the state capital after attending a 9/11 anniversary ceremony in New York City. He arrived at the event via ferry, said his spokesman, Colin Reed. The governor’s office said Christie never shared a helicopter with David Wildstein, his former No. 2 man at the Port Authority, who oversaw the lane closings and has since resigned.

A photograph taken at the event – held on the third day the lanes were blocked – shows Christie walking with Wildstein and other close allies at the authority.

Two traffic lanes leading to the bridge were shut starting Sept. 9, creating gridlock in Fort Lee, the town at the base of the bridge.

The Legislature is investigating whether the closings were engineered to send a message to the community’s Democratic mayor, perhaps for not endorsing the Republican governor’s re-election bid.

Christie has maintained he was unaware of the lane closing operation until after it ended. He added last week that even if he was told or read about traffic jams while they were happening, the information didn’t register as being unusual.

Wildstein, who is seeking immunity from prosecution, recently claimed through his lawyer “evidence exists” that Christie knew of the lane closings while they were happening. He did not identify the evidence.

The legislative panel deliberated for two hours behind closed doors Monday before emerging to pass six motions rejecting requests by lawyers for former Christie campaign manager Bill Stepien and fired Deputy Chief of Staff Bridget Kelly to withdraw document subpoenas.

Lawyers for the two said the subpoenas were overly broad and interfered with their rights against self-incrimination.

The panel deemed its request for emails, text messages and electronic correspondence necessary and authorized its lawyer to set a new date for compliance after agreeing to minor modifications in the two subpoenas.

Four Republicans on the panel abstained, saying they were not given ample time to review the complex Fifth Amendment arguments.