The judge in the trial of a man accused of throwing his fiancee off a Sydney balcony has asked the Seven Network not to proceed with the airing of a story tonight, amid concerns it could include evidence not heard in court.

Simon Gittany is on trial for the murder of Lisa Harnum, who fell 15 floors to her death in July 2011.

The 40-year-old's barrister has expressed concern that Gittany was approached by a journalist from Channel 7's Today Tonight program outside court.

The female journalist allegedly asked him why he had been so "jealous" and "controlling" in his relationship with Ms Harnum.

The court heard that the journalist then told Gittany a story would be aired this evening.

The journalist allegedly approached Gittany with a microphone and multiple cameras.

A preview claims the story will reveal "explosive new evidence", which lawyers say could be in contempt of court.

Supreme Court Justice Lucy McCallum called the behaviour "appalling" and immediately adjourned to discuss the matter with the Chief Judge.

When Justice McCallum returned, she said the producer of the program would be contacted and asked to attend court "as a matter of urgency".

The judge told the court the program had the prospect of "interfering with the administration of justice".

"It shouldn't have happened, and I shall do whatever is in my power to ensure it doesn't happen again," she said.

Crown prosecutor Mark Tedeschi QC said the information potentially disclosed in the program is "highly inappropriate during the course of a criminal trial, and could amount to contempt".

Lawyers representing the network have attended court, and were asked to instruct the producers not to air any footage of Gittany filmed this morning.

Justice McCallum also told the lawyers that the program must not speculate on the case and could only report the evidence heard in court.

She said it would be inappropriate for the lawyers to divulge any information about the story, given that it was a judge-only trial.

Counsel for the Seven Network, Sandy Dawson, made an assurance to the court.

"I am instructed to offer all of those undertakings," he said.

A producer for Today Tonight has apologised in writing to the Supreme Court. The network now says it will only report what was said in court.

The trial continues.