It is believed that Webb's customers were approached by email and telephone to buy and sell their art through Bowerbank Ninow.
In the high-end art world, confidentiality and discretion are highly valued, with many collectors staying tight-lipped about their sales and purchases.
Customers were understood to have been disgruntled that Webb's had breached their privacy by giving up their details - but the auction house was said to have been baffled at what was going on.
It was allegedly discovered that Webb's database had been downloaded or copied from a computer and put into a cloud-based storage system, and police were called.
On Thursday the company that recently bought and sold Webb's, Bethunes Investments, lodged a market notice on nzx.com.
"[Bethunes Investments] has lodged a complaint with the NZ Police with regard to the conduct of two former staff of its former auction business operating under Peter Webb Galleries Limited," the notice said.
"This complaint relates to what we believe was misuse of intellectual property owned by the business," it said.
"The relevant events arose prior to the business being sold earlier this year, this matter was an excluded item from the sale and accordingly this matter does not involve the purchaser at all," the notice said.
We are currently consulting with legal counsel and we plan to rigorously defend these allegations.
The company, which sold Webb's to Mossgreen NZ in January, said in the notice that it was also considering Employment Relations Authority proceedings.
The company did not wish to comment further.
When approached by the Weekend Herald yesterday, Mr Ninow said in a statement on behalf of himself and Mr Bowerbank that they would answer questions in full at a later time.
"In the meantime I can say that we are currently consulting with legal counsel and that we plan to rigorously defend these allegations."
Bowerbank Ninow has been praised for offering a voluntary resale royalty of 2.5 per cent of the hammer price, paid at no cost to the vendor or buyer, of any work by a living artist at auction.
Mr Bowerbank and Mr Ninow both have impressive resumes, with tertiary qualifications and experience managing, and selling works by, some of New Zealand's most prominent artists.
