Current and former public servants told the Independent Commission Against Corruption (ICAC) on Friday that Mr Maguire's alleged threats could have "embarrassed" NSW in front of the Chinese government if he had refused to back down.

Charles Cull, a former senior advisor to NSW trade minister Niall Blair, told ICAC he met with Mr Maguire in August 2017 over concerns that United World Enterprises (UWE) would have to close its Riverina oaten hay export operation.

UWE managing director Jimmy Liu previously told ICAC that his business was "suffering" because majority shareholder Bright Food, a Chinese company, was planning to pull out of the Leeton joint venture.

Mr Cull said Mr Maguire provided an "appalling" draft letter, which he intended to send to Shi Mingfang, a Chinese Communist Party committee secretary and Bright Food board chairman.

"It was very provocative in the language involved," Mr Cull said.

Mr Cull said Mr Maguire's letter warned of a "loss of face of political leaders" and that the Leeton business collapsing would question "future joint ventures" with Chinese companies.

Mr Cull said his department contacted the federal Department of Foreign Affairs and Trade due to Mr Maguire's "intense and erratic" behavior and he feared Mr Maguire would "cause some trouble".

ICAC is investigating allegations that Mr Maguire used his public office for personal gain between 2012 and 2018.

Mr Liu told ICAC he was "friends" with Mr Maguire and admitted he paid Mr Maguire $1400 and covered his costs for a trip to China in 2014.

Sarah Cruickshank, former chief of staff to the NSW Premier, told ICAC that it was "completely inappropriate" for a backbench MP to contact a foreign government and threaten to cut off future business in the state of NSW.

Ms Cruickshank said Mr Cull told her at the time "Daryl has threatened to go to China and the minister is concerned it will affect the trade mission".

"I said to Charlie 'that's ridiculous, Mr Maguire can't do this," she told ICAC.

Ms Cruickshank said it was "not unusual for an MP to be fervent about an issue" but it was unusual to make "a threat to get on a plane".

Ms Cruickshank told ICAC it was a "pretty serious" situation and she would have spoken to legal counsel if Mr Maguire had not backed down within "12 to 24 hours".