By Joseph Ax

NEWARK, N.J. (Reuters) - Closing arguments in New Jersey's "Bridgegate" trial were unexpectedly postponed by a day on Thursday because of an unspecified "legal issue" that must be resolved, the trial judge said.

U.S. prosecutors in Newark had been scheduled to begin summing up the evidence against two former allies of Governor Chris Christie who are accused of orchestrating lane closures at the busy George Washington Bridge to New York City in September 2013 in an act of political retribution.

U.S. District Judge Susan Wigenton told jurors to return on Friday morning for closing arguments, which are now expected to last into Monday.

Prosecutors and defense lawyers, who also left for the day, declined to comment on the nature of the issue.

Jurors have heard more than a month of testimony in the trial of Bridget Anne Kelly, Christie's former deputy chief of staff, and Bill Baroni, former deputy executive director of the Port Authority of New York and New Jersey, operator of the bridge.

Prosecutors say the two conspired with another Port Authority executive, David Wildstein, to create massive gridlock in Fort Lee, New Jersey, to punish the town's mayor for refusing to back Christie's 2013 reelection campaign.

The scandal damaged Christie's political standing as he was beginning a campaign for the Republican presidential nomination. The governor is a top adviser to Republican presidential nominee Donald Trump.

Christie, who has not been charged with wrongdoing, has said he was unaware of the lane closings at the time.

But testimony at the trial from several witnesses have contradicted Christie's claim.

Wildstein, who pleaded guilty and testified for the government, said he and Baroni discussed the plot with Christie as it was unfolding.

Baroni and Kelly each took the stand and said they spoke with Christie about the lane closures, though they said they believed that the closures were part of a legitimate traffic study.

Kelly, who cried several times during her testimony, portrayed Christie as a demanding and bullying boss who once flung a water bottle at her in anger.

She was the author of an infamous email sent to Wildstein that said, "Time for some traffic problems in Fort Lee," a message prosecutors say set the scheme in motion.

But Kelly told jurors that she was simply parroting the language Wildstein had used in describing the potential gridlock caused by what she believed was a Port Authority-approved traffic study.

(Additional reporting by David Ingram in New York; Editing by Scott Malone and Steve Orlofsky)