He's been on a luxurious international sojourn, but it was back to the inside of a Sydney courtroom for controversial property developer Salim Mehajer​ on Tuesday.

And it wasn't good news for the former Auburn City Council deputy mayor, with prosecutors revealing there is a fresh investigation under way that could see him charged with more offences relating to electoral fraud.

Last year Mr Mehajer was charged with more than 100 offences relating to his alleged rigging of the 2012 council ballot, including using forged documents, making false statements and giving false or misleading information.

His sister Fatima has also been charged with a string of similar offences, which carry a maximum penalty of 10 years in prison.

In the Downing Centre Local Court on Wednesday, prosecutor Michelle England said there was a new investigation under way that could see Mr Mehajer face even more charges.

"It appears that further serious criminal activity has been engaged in, in furtherance of that electoral fraud," Ms England said.

"It's not yet clear who is responsible for that behaviour."

Mr Mehajer's brother-in-law, Jamal Elkheir, and five others who ran as candidates in the poll, were facing charges of producing a false or misleading document but these charges have since been withdrawn.

Developments in the co-accused's matters, the court heard, relate to the new investigation.

A handful of charges have also been withdrawn against Mr Mehajer, but the bulk remain.

Ms England and defence barristers for the Mehajer siblings all submitted a joint application to adjourn a two-week-long hearing into the matter that was due to start next week.

The court heard that Ms Mehajer, who is 23 weeks pregnant, was suffering from a medical condition that would make it "untenable" for her to sit through the hearing.

Nearly 150 witnesses would be required and the hearing would take as long as eight weeks if it went ahead presently, the court heard.

A new timetable for the case is due to be set down early next month.

Mehajer, 30, who is due to release his own toiletries line, has previously brushed off the electoral fraud allegations.

He told Fairfax Media last year it was "all a political game targeting Auburn Council as a whole; just like how we were confirmed to merge with Strathfield, Burwood and Canada Bay" and now Holroyd Council.

"Welcome to politics," he said. "It's full of hidden agendas to make me step down."

He questioned the strength of the AFP's case, saying the matter was "open in 2012".

"If their case was strong, they would of [sic] not let me sit a day on council," he said.

"I sat four years as deputy mayor, so why didn't they act earlier, when the case was open and when I personally contacted the AFP many times in 2012, 2013 and 2014 to take this matter seriously and deal with it as priority?"

He is, however, no stranger to the legal system. His apprehended violence order disputes with his estranged wife, brother-in-law and Bruce Herat, the father of Sydney siege victim Joe Herat, have been well documented.

Footage also last week emerged of him being arrested in Ibiza.