Sydney developer Jean Nassif and his company Toplace can continue to operate while the decision to suspended their building licences is reviewed, a tribunal has ruled.

Mr Nassif and the company have successfully argued for a stay on the bans before the NSW Civil and Administrative Tribunal (NCAT), which heard the suspensions exposed the parties to breaching contracts worth tens of millions of dollars.

It would also jeopardise remediation works for 899 units which were either under repair or set to have defects fixed within Toplace projects, the developers argued.

In December, NSW Fair Trading moved to suspend Mr Nassif for 10 years and permanently revoke Toplace's licence after finding them guilty of improper conduct.

NCAT Acting Judge Terence Simon today, however, ordered Mr Nassif and the company can operate, while a review of Fair Trading's decisions takes place.

But he ruled Toplace couldn't take on new contracts without the approval of NCAT and the Commissioner of Fair Trading.

The judge found the cancellations would have a "significant effect" on the "applicants, parties with whom they have contracted or have arrangements to undertaking rectification work and the applicants' subcontractors and employees".

"This is only an interim application, the evidence in relation to the Nassif and Toplace decision has not yet been provided, challenged or conclusively examined by the Tribunal," his judgement stated.

"There will need to be in this case, an evaluation of the seriousness of the alleged breaches and the evidence overall."

NCAT had heard Toplace has two Sydney projects under construction, Skyview at Castle Hill and a development at Box Hill respectively, for which contracts have been exchanged with homebuyers.

Those contracts are worth more than $74 million and $48 million respectively, the tribunal heard, and would be "in jeopardy if the stay is not granted".

It was also argued that Toplace faced a bill of between $144 million and $147 million for present and future subcontractor work.

The projects' financiers, the National Australia Bank and PAG, had also asserted the bans constituted a "very serious breach" of their financial arrangements, NCAT was told.

"I am satisfied that should the Toplace and Nassif decisions take effect, it will result in Toplace Pty Ltd breaching contracts which are currently on foot and breaching the requirements of finance facilities funding the current projects," Acting Judge Simon wrote.

The suspension notices came after an investigation by Fair Trading, which alleged it had found more than 40 defects in residential developments constructed by Toplace: the Atmosphere and Skyview developments at Castle Hill, and, the Vicinity building in Canterbury. 

NCAT has heard Toplace will lead expert evidence to show that "many of the alleged defects either never were or are no longer defects".