The frustrated boss of NSW's anti-corruption commission has repeatedly accused a witness of lying and obstructing the inquiry into the NSW Labor donations scandal.

Alex Wood, formerly known as Alex Wu, is being investigated over his alleged role in a scheme to mask the true source of a $100,000 donation to the NSW Labor party in 2015.

Two of the 12 straw donors subject of the NSW Independent Commission Against Corruption inquiry worked at Mr Wood's property developer Wu International Investments at the time.

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"I don't know how many times I have to say it to get it into your head," ICAC Chief Commissioner Peter Hall QC told Mr Wood on Thursday.

"You are here under an obligation to be truthful, to cooperate with the Commission, not to lie, not to obstruct, not to interfere. Do you understand?"

Mr Wu, who denies any wrongdoing in the scheme, replied: "Yes. I try the best."

The repeated instances of "I don't recall" and "I don't know" led to counsel assisting Scott Robertson to ask the 36-year-old: "Do you have dementia or another condition affecting your memory?"

"Not at this point," Mr Wood replied via a translator.

"I think I have a pretty good memory but sometimes I just forget about something."

AAP

A former employee of WII, Steve Tong, told ICAC in August he didn't donate $5000 to Country Labor in 2015 and was dumbfounded when he received a tax invoice for it weeks later.

In an email to Mr Wood shown to ICAC on Thursday, Mr Tong accused Mr Wood of using his name on the donation form and said Mr Wood had failed to take care of queries about the donation from the NSW electoral commission.

"You lied," Mr Tong wrote in the 2017 email.

Mr Wood said the email itself was made predominantly of lies but he'd not yet replied to Mr Tong in person, over the phone or in writing.

Mr Hall said that was "amazing".

"If this man was raising all these concerns, saying 'I'm being taken for a ride, someone's used my name', he's accused you of lying and you don't even respond?" Mr Hall said.

Mr Wood said he asked his deputy to address the matter with Mr Tong, adding the former employee had heart problems and "I didn't want to argue with him".

Mr Wood agreed to hand over his email password and allow ICAC to search for particular emails of interest held in WII's offices.

He is expected to be recalled to give evidence at a later date.

The inquiry continues.