Ian Robertson told the Independent Commission Against Corruption on Monday he's certain he would remember a meeting with Ms Murnain about false donors, Chinese billionaire Huang Xiangmo and $100,000 in cash.

"That is simply extraordinary and I'm certain I would have remembered it and I'm equally certain I would have told her that it would have to be dealt with quickly involving the electoral commission," Mr Robertson told the inquiry.

The ICAC is examining whether Mr Huang, who is now banned from Australia, was the true source of $100,000 said to be donated to Labor by 12 people at a 2015 Chinese Friends of Labor dinner.

Mr Huang, a property developer, was prohibited by law from making donations to NSW political parties.

Ms Murnain previously told ICAC she met with Mr Robertson on September 16 in 2016 after upper house MP Ernest Wong told her about a potentially illegal donation made by Mr Huang.

The now-suspended party boss said she connected the donation to the 2015 CFL dinner.

In her evidence, Ms Murnain said Mr Robertson advised her during the September 16 meeting to "forget the conversation happened".

But Mr Robertson on Monday said he had no recollection of the meeting and would never advise a client to behave that way.

"If Ms Murnain, who is the general secretary of NSW Labor and one of the most important people in Labor nationally, had come to see me, to tell me about fake donors and donations and Mr Huang, I would firstly remember it," he said.

"I categorically deny advising her in any way it should be covered up."

He said he "strenuously denied" what Ms Murnain alleged.

When asked by counsel assisting Scott Robertson if Ms Murnain ever discussed with him an issue relating to Mr Huang, the lawyer insisted he didn't recall.

But, Mr Robertson said, he "very much" wished she had.

Mr Robertson - a senior partner with Holding Redlich - told ICAC that although he has no recollection of the alleged events on September 16, his office security card records are consistent with Ms Murnain visiting him that night.

However, he claims if the meeting did happen, it would have been about a different matter - whether a company had paid for former Labor MP Nick Lalich to travel to China.

Mr Robertson earlier told the inquiry a December 2016 letter from the NSW Electoral Commission requesting information about the CFL dinner was the first time he became aware of the donations issue now being investigated by ICAC.

Mr Robertson's lawyer, Tony McInerney SC, last week accused Ms Murnain of telling a "pack of lies" to the ICAC.

Ms Murnain insisted she wasn't lying but admitted that by not revealing her knowledge of the donation she cast an unfair shadow over the party and its members.

She was suspended from her role as general secretary after telling the inquiry she knew about the suspected illegal donation for nearly three years.

The inquiry continues.

Australian Associated Press